It's fair to distrust something because you were burned by using it in the past. However, both the examples you named -- Postgres and FoundationDB -- have had similar concurrency and/or data loss bugs. I have personally seen FoundationDB lose a committed write. Writing databases is hard and it's easy to buy into marketing hype around safety.
I think you should reconsider your last paragraph. MongoDB has a massive community, and many large companies opt to use it for new applications every day. Many more people want to use that product than FoundationDB.
I think you should reconsider your last paragraph. MongoDB has a massive community, and many large companies opt to use it for new applications every day. Many more people want to use that product than FoundationDB.