Not sure it's possible to avoid entirely, as the community here grows we get more of all types, it's hard to have a truly only-positive community when moderation is voluntary and the masses have full reign to submit literally anything.
Do you think a technology solution would help? Sentiment analysis on posts and gently redirect people to other communities instead of outright blocking them?
Maybe the only real solution is personal resilience and recognizing that we don't need to feel negative feelings just because we received a negative communication