Some accounts are deleting their posts after a few downvotes. It’s devastating on communities like c/asklemmy.
Lemmy doesn’t track an account’s karma like reddit. So, all downvotes will be isolated to your post or comment and won’t affect your account—unless you wrote something truly horrible.
Remember lemmy is a community effort. Deleting a post also removes all comments on it. So you are not only robbing the effort others put in, you are actively removing knowledge from the fediverse. Others won’t be able to find it through search and lemmy will seem lonelier than it already is.
I hate to say it but I think that’s the point of why some people, mostly bots, brigade.
Imo, it’s a 4chan/discord/twitter style of attack to foster cult-like behaviors. It’s often purposeful done to drive out dissenters and it simultaneously makes it appear like your opinion is widely shared, while in reality it could be a very vocal minority, alt-accounts chiming in, or bots doing the brigading.
Many Lemmy communities have done a decent job so far at keeping bots out imo, which is something other social media platforms like Reddit don’t even attempt at doing at scale since it inflates active account numbers.