You're completely right, of course; however, no, I don't intend it as a scientifically rigorous experiment. Actually, I'd like to see what happens when people whose most controversial opinions are NOT worthy of explicit disdain (such as racism or sexism) discuss their controversial opinions. Hubski is implicitly not a welcoming community to people who seek to offend or who are seeking microcosms online where opinions considered repulsive in the mainstream are heartily seconded, thirded, and more. (See: r/MensRights) So, it's not an experiment comparing Hubski and Reddit, necessarily. It's an experiment comparing a context explicitly welcoming to racism, sexism, classism, and so on and so forth, vs. the question of controversy posed in a context explicitly unwelcoming to the same.
Yeah, if I had to answer this myself I would say that being even slightly open to religion as a positive factor in human lives is probably my most controversial opinion, because I'm so on the fence there that the Internet hates me for kind of liking religion, and the Bible Belt would consider me a heathen for not being sold on it entirely. That and my own brand of religious experimentation is explicitly interfaith, so if you hate Christians, Jews, OR Muslims you're not allowed to like me!
I think the problem is that by picking a side in religion you're standing up and saying "I think this is the right choice". Which means you think all the other choices are wrong. Which in the modern world is probably the worst thing you could do, that is, be judgmental.