Way too many, and you wouldn't think it would be as big of an issues as it is. It's been this way for decades.
Is it inconsistent referees? Is it lack of coaching/discipline?
I get the feeling that coaches don't even get that upset by it, as compared to other infractions. That would indicate it's more of a problem with the rules being subject to "judgement". Perhaps it's just one of those things where the NFL believes any substantial change would give one side a clear advantage over the other, or possibly lead to more injuries.