Directing negative feelings to others who didn't actually wrong him is bigotry, though, isn't it? If a black man mugged my uncle, would it be ok to slag off all black people?
You are missing the point. To use your analogy would it be acceptable to be a bit off with people going around wiyh stickers saying muggers are heroes? The story of the British army in ireland is not a wholly honourable one. If someone grew up experiencing them as an occupying army we should cut them a bit of slack when we spend a month glorifyimg them. This does not mean we should stop wearing popies or anything like that just that we should not have to resort to insults for someone with an opposing view.