Prejudice

Since I'm part of an ethnic AND religious minority, I'm fully aware of how wrong prejudices are. Often I can understand what causes such thinking and sometimes I won't even blame people thinking that way.
BUT: What on earth causes justifies me, a victim of prejudice myself, to have prejudices against others???
That's just not right, it's plain wrong.
I realized it last week. I was about to buy a second hand tablet-pc and I got in touch with one German engineer (I know that from his automatic e-mail signature) and one rather young Russian with a barely any complete sentence and a rather heavy accent on the phone. Even though the price was the same for both, both objects had some pros and some cons for them (be it accessories or the location where to pick it up), I still refused to call the Russian a second time... only for my damn prejudices!
This is just wrong. And that's why I'll call him now.