@sunnySkys - I would say that it is actually natural for people to develop an "us versus them" mentality. That's why there are laws to protect people's freedoms. There will always be people who act in a prejudiced way, in any country and in any time in history.
The main difference is now there are the laws to prevent people from acting in a bigoted way. In some cases the laws need to be expanded, but the basic goal of liberty and pursuit of happiness for everyone is a wonderful thing to keep in mind and aim for.
You're right though, it is interesting how the Irish went from being such a hated group to being just one more part of the mixing pot.