I believe Lemmy has the potential for a wider range of discussion and debate than Reddit, or any other social media platform I've been on, simply because of the defederated & community-based system. The issue, as you describe, seems to be saying the wrong thing in the wrong place, which, to be honest, is similar to the real world. There are a lot of topics people probably shouldn't talk about in public, but it's normally fine for them to talk about in their chosen groups/community. Lemmy just kind of brings these groups and communities closer together, igniting more discussion, but simultaneously causing issues you describe.
For example, you can't walk up to a group of homosexuals and try to convince them they shouldn't be gay. You can discuss topics related to LGBT+ rights of course, but there are definitely off-limit discussions in that group, same as any other group. I think it's a matter of paying attention to where you are in the Fediverse and who may be reading your response before blurting out what's on your mind.
On the comment about tessaract; I cannot agree on the idea that the dev of tessaract was "right" about toxicity. Even if he was, he was in no place to take it into his own hands to address (especially in a secretive way). Lemmy is a community-based platform and we need to figure that stuff out as a community. We don't have a corporate-level moderation team ensuring the platform is safe for those under 18, and we don't have anyone enforcing political views in any way other than in specific communities (who have every right to enforce their chosen views). Just as some say we wouldn't need police if we had strong communities, the same goes here, strong communities are the key. If you see a lot of toxicity where you browse, maybe your chosen community just isn't a healthy one.