Many people in DF do not respond to the good tone - they want drama and make a fun of others (due to boredom) and just need a reason to do so.
The less i speak - the less they will notice me and i will keep more reasons to remain silent when directly addressed. In such team everything i say will be used against me (like replying in a troll thread).
There are people with more serious issues like a feeling of being outcasted, but are rare compared to people who just want drama.
The way i worked out to make the team cooperating again is to direct their wasted energy towards solving a hard task such as completing a dungeon without a tank/healer (which is entirely possible), so they have to either start cooperating or leave.
I have no idea what to do if someone feels outcasted though. For some reason many people have an offensive style of speech (i blame american cartoons and social networks tbh) which many would not accept, so their communication attemps will fail.