It's a problem in academia as well, there's a new journal launching to help combat that problem https://www.bbc.co.uk/news/education-46146766
Well, maybe within the scope of the question as defined by OP since it explicitly begs for controversy. But should you expand it to the broader What is an idea you hold that runs contrary to the common wisdom of field X? Then suddenly it becomes a lot more interesting and fruitful,
It's not that heterodox political opinions are intrinsically less interesting but few people know how to discuss them constructively, much less online. That breeds low quality discussions where everyone is at each other's throats. Broadening the question has at least the merit of being less polarizing without giving up on critical thinking, or bravery. Ultimately, the goal is the pursuit of the truth - something that breaks mimeticism (or kickstarts it).
I dunno... I'm pretty honest here, especially when taxation and gun control come up, and I haven't been kicked. I get downvoted to oblivion every now and then, but I've got enough Imaginary Internet Points to burn 'em for heat (so to speak) so not a real big deal.
If you're looking for something not political, I'd go with something like:
1. The web-browser shouldn't try to be a knock-off operating system, and should delegate many things to native code using protocol handlers or some-such.
2. Groovy is a totally badass programming language and is way under-appreciated today.
3. The Semantic Web vision remains alive and is continuing to develop and is one of the most important initiatives out there, short of us developing AGI.
4. An AGI might have "human level" intelligence in dis-embodied form, but I believe an AGI would need to be embodied and sense the world somewhat like the way we do, to truly have "human like" intelligence.
2. Abortion is murder and but that doesn't mean it it should be made illegal. The government sanctions killing of others through acts of war, self defense, use of deadly force. The historical precedent of the economic, public health and social impact of banning abortion make banning abortion against the function of most governments. The government should not be morality police, but a hockey-style referee for economics and public safety.
I got tired of explaining my stance on the second issue to the point to where I just say that citizenship is issued on birth in USA therefore fetuses aren't citizens and prioritizing the fetus over the mother is a homeland security issue.
Second most controversial opinion: The Last Jedi was a good film. Flawed, yes, but not deserving of the hate it's gotten.
But yeah, The Last Jedi was frickin' awesome.
My most controversial opinion is likely that any law that give gender, race and religion special treatment is discrimination that promotes tribalism and polarization.