Quite aside from the impact on one’s fellow human beings, this kind of behavior can come back to haunt the individual far into the future. What if a person applies for a job and the potential employer decides to Google just to see if there’s any further indications of personality, behaviors, etc., as part of the “getting to know” process? Moving a team forward (whether FOSS, paid job, whatever) is all about what the team can do. Uncooperative, dismissive and anti-social behaviors are toxic to a team.
This can have a negative impact long after (theoretically, and even if) a person changes their behaviors. I was a part of an employee search when we ended consideration of an individual because, despite their known technical qualities, they weren’t a team player. In that case it wasn’t really acrimonious – that individual actually enjoyed a good argument and usually ended up doing things their way. From their POV it wasn’t a negative thing, but it wasn’t team-friendly and they missed consideration for the job because of it.
To paraphrase Marc Antony, “The online behaviors that men do lives forever after them; the good is oft interred with their bones.”