There is absolutely, unequivocally nothing illegitimate about keeping track of seen cards in blackjack. There is also nothing illegitimate about the casinos not allowing you to play. They do this not because playing with an advantage is illegal or "illegitimate", its just that they don't want anyone playing who isn't going to lose in the long run. It is perfectly legal to count cards. This has been upheld in several court cases. In fact, in Atlantic City they can't even ask you not to play if they *know* you are counting (but they make the game unbeatable in other ways).

I typed up a long message responding to the rest of your points, but lost it to a misclick. Maybe I'll do it again later. The bottom line is that online poker is real poker, it is safe and your concerns are not practical concerns in real life day-to-day play. Maybe I'll write the whole thing up again if there is some interest. Your "assurance" is your knowledge of the game, the ability to assess your opponent's play, and to keep statistics on your own play. Results don't lie (at least, long-term results don't!)