I don't know whether I'm a reliable source to answer this question because I'm very jaded about this in general. A couple of days ago, someone on the Sri Lanka Reddit started up discourse about Maitreyi Ramakrishnan's choice to reject identifying with the country that tried to genocide her people, which I'm still chewing wire about. I'm a very isolated person with a very small social circle of like-minded leftist friends. They're mostly not SinBud and anti SinBud nonsense, but none of them are Tamil and I'm the one who really convinced them about Eelam I think. The people I learned from, who are out there doing the work of building inter-ethnic dialogue and overturning Sinhalese propaganda, might have a more hopeful view.
Thing is, there's no one "leftist" faction here because "left" doesn't mean the same thing as it does in the West. The Rajapaksas' party SLPP is socialist, a legacy of their ancestor the SLFP who was the party aligned with the USSR. They and their voters and their saffron terror acolytes (Buddhist priesthood) are all for public infrastructure they can rob blind and central government they can use to crush minorities, and build on the nationalist fervour of genocidal Sinhalese Buddhism that's served both major parties independence. There's quasi-communists, descendants of the ethnonationalist Marxist JVP that rose in opposition to the class corruption of ethnonationalist USSR-aligned socialist SLFP and enthonationalist US-aligned neoliberal UNP. They've since distanced themselves from their ethnic myopia, possibly due to suffering much of the same state terrorism as minorities via militarisation and policies like the draconian Prevention of Terrorism Act. They're the most vocal about the abolition of the executive presidency, the defunding of military and police, and restructuring and executing the long-mismanaged socialist infrastructure. These are usually the working class and university students, but their base has been growing in other demographics too, since we "held our noses and voted" for the Yahapalana government in 2015 and it ended up fucking us over. But despite their sympathy with the suffering of Tamils and Muslims and favouring the devolution of power, most still cling to the idea that Sinhalese majoritarianism is a fair result of democracy.
The kind of pro-LGBT, anti-racist, feminist liberals that would pass muster with the western left otoh, are a minority of urban, English-speaking professionals. Their panacea for enthofascism is voting for the neoliberal party, whose idea of reducing corruption and increasing efficiency is privatizing everything, are against racism because it's bad for tourism, and coasts on the promise of never actively feeding ethnosupremacy, even if they won't do anything about it either. Both these groups hate each other but are equally deeply uncomfortable with if not entirely resistant to the idea that the North and East are Tamil lands colonized by the Sinhalese. Both groups are aware of the corruption and complicity of the Buddhist priesthood and are prepared to do exactly nothing about it.
What I'm trying to say is that Sinhalese Buddhist ethnosupremacy is baked in to the Sri Lankan political fabric. "Left" means jack shit when it comes to whether Tamils have rights, in much the same way that the western left agrees on everything except Palestine. It's a political no man's land everyone tries not to look at.
The fundamental problem is that Sinhalese people who know enough about 1958, 1983, or the full scope of genocide perpetrated against Tamils during the last push of the war, let alone all 26 years of it, are very much in the minority. It takes a particular education to understand that "Sri Lanka" is a post-colonial invention that took over from "Ceylon", which was nothing but a construct for the ease of British administration. As far as I know, this education is confined to activist organizations and whoever followed my sociology program. So my kind of anarchist leftism that calls the war a Tamil genocide with their whole chest and the priesthood saffron terrorists and recognises Eelam is, afaik, vanishingly small.
To be honest, I never really questioned the propaganda and narrative we've been spoon fed myself until I went to Canada when I was 23 to complete my anthro degree (became disabled and dropped out after). One thing that struck me was how racist the Sinhalese diaspora was. I was raised SinBud, my school didn't admit any non-Sinhalese, half my uncles were in the military, but these people that had left the country decades ago still hated Tamils and Muslims in a way that nobody else I knew did. I wondered whether this was what it had been like when it had all started; whether this hatred that seemed to have been preserved in amber was a true taste of what had ignited Black July. Suddenly the attitude of the Tamil diaspora towards the Sri Lankan government and Sinhalese people didn't seem so unreasonable.
Then, later in the same uni term, I went to an art exhibition of a white artist who travelled the world collecting information about their genocides and made art about them, and found a painting depicting Sri Lankan Tamils in 2008. Promptly had a meltdown. Went to the lady and told her tearfully that it was all propaganda, we didn't really hate Tamils, not even my uncles in the army hated Tamils, it was a war, the LTTE had terrorized us for my whole lifetime. Bless the woman, she didn't fight me, just let me cry at her and patted my hand and pretended to take me seriously. This made it easier for me to really think about what I knew once I'd stopped wailing and stamping. It prompted a years-long self-interrogation and fact finding that made me unearth how much brainwashing had been done to us by everyone, from our families to our school textbooks to news media. It's like the air we breathed was propaganda. And I still didn't know a fraction of what life had been like for Tamils (or Muslims) and the scope of atrocities perpetrated by the Sinhalese until I began my Society and Culture degree at the Open University when I was 30. The first year textbooks were only broadstrokes facts, but at last I found out about Gnananth Obeysekera, Prageeth Jeganathan, Stanley Thambaiya, Malithi DeAlwis. Their work on nation-making, ethnicity, historical revisionism, genocide and ethnic conflict and state terrorism...everything I should have been taught as a child. The chapters on the rapes and murders and shelling and war crimes and IDP camps were..indescribable. That was what properly radicalised me about Tamil self-sovereignty, because there's clearly no possible way the Tamil people will ever be safe and safeguarded under a Sinhalese majoritarian government.
I had to drop out of that programme too because of my health. But during the mass protests against the government in 2022, I learned even more about Tamil indigeneity, the extent of JR Jayawardena's crimes, and the persecution of Marxists and victims of the '71 and '89 insurrections. So much of the protests and their encampments were directed and galvanized by social media, that organised online and in-person lectures, teach-outs, and live discussions that anyone and everyone could attend right alongside the protests. I've never seen that kind of truly democratized, free, egalitarian civic education and discourse before. That was the very first time I saw academics, survivors, refugees and human rights activists being given a respectful platform, the masses hearing firsthand accounts from people of the North and East and witnesses of Black July. April to July 2022 was a truly golden bubble of time where I saw people finally start listening, believing, and challenging all their convictions. It was the closest we ever came to realising the hope that things could be different; that we could, as a society, understand how Sinhalese ethnosupremacy had been the black rot killing this country from the first, stop being racist Sinhala-first cunts and actually hold any of these murderers accountable.
Teach us to hope, I guess.
But I suppose it's no small thing that I learned about the Tamil resistance and struggle and taught all my friends about it. I'm sure they're informing their own circles in small ways too. These tendrils are hard to see, but they exist and grow. Especially with the fall of the Rajapaksas and their Bhaiyya contingent, more people can see ethnosupremacy for the grift that it is, and the younger generations are less defensive, more willing to listen and eager for justice and change. So I guess the answer is: not very common, but less uncommon than it used to be.