Maybe I'm making a generality of a few fringe cases but since 9/11, and the rise of TSA and several horror stories of Police abuse I abandoned my project to one day visit this great country.
Bill Clinton once said "There is nothing wrong with America that cannot be cured by what is right with America", and at the time I agreed with that. It has been a while since I do not believe this anymore.
I believe the likelihood of having a serious run-in with the law in the U.S. as similar to having an accident when doing an "extreme" sport - you have to be aware of the possibility when doing it and accept them, but they're not so bad.
The most likely scenario, from what people who visited experienced: you will be treated a bit roughly at customs/inmigration (fingerprints, questioning your motives) and then you'll be free to have a nice time.
Do your homework and have your visa and papers and travel schedule and hotels in advance, and you'll be fine. It's still one of the least friendly countries to enter (and that's validated by people I know that have visited 100+ countries, I've visited 50+ myself), but I think it's worth it and I'll visit someday.