Why do people dislike Gypsies in Europe?

I'm American but have been to Europe many times. Last year when I was in Belgium wih my family (my dad is French-speaking Moroccan so he works there), there were quite a few gypsies in Brussels. People don't like them because they beg, and often trick people and scheme to steal things. They cause a lot of problems and live off of others especially in big European cities. A lot of them are thiefs and thats how they get by. I've seen them pickpocket people quite a few times so I'm always cautious around them