You have no idea what you are talking about.
> On the other hand in most of the European countries criminal records are limited and after X years they disappear and you can't legally discriminate based on that.
This is something that varies state by state in the United States. In general, misdemeanors can be removed from your record faster than felonies and if they could they'd put a big red 'A' on your chest for sex crimes. Some places will clean your record automatically and some will requre you to contact the courts. But again, varies state by state, or even county by county.