A fourth option, online community specific, could be something like this: Allow members to post their comments anonymously, under following conditions:

Only users with enough karma can post anonymously. (This is to prevent abuse by trolls.) You pay some karma for posting anonymously, which is a constant number not depending on whether people agree with you or disagree with you. (To prevent abuse by serious members.) If you comment anonymously again in the thread below your original anonymous comment, you don't pay karma again, and the website shows that this is the same anonymous person, for example by using "Anonymous#1". (So for example people can ask for clarifications and you can explain freely.)

The anonymous comments can also be upvoted and downvoted, and hidden if they get too much downvoted, but their karma is not reflected on their user. Also, the social effect is that other people don't know who you are, even if they downvote you.

I don't know how much useful this would be. The feeling of being downvoted could still be unpleasant. But it would be some balance between the ability to write anonymously, and possible troll abuse.