I wonder if part of the problem might be a natural tendency to generalise bad behaviour of a small number onto the whole group?
For example, I might see several instances of individual cyclists running red lights and generalise that to "all cyclists run red lights". Or see several instances of individual motorists "dooring" cyclists and generalise that to "all motorists are dangerously inconsiderate".
It's probably easy to go from that generalisation to an overt dislike of the other group. Therefore, I try to force myself to attribute bad behaviour to the individual rather than any groups they might be a member of.
For example, I might see several instances of individual cyclists running red lights and generalise that to "all cyclists run red lights". Or see several instances of individual motorists "dooring" cyclists and generalise that to "all motorists are dangerously inconsiderate".
It's probably easy to go from that generalisation to an overt dislike of the other group. Therefore, I try to force myself to attribute bad behaviour to the individual rather than any groups they might be a member of.