Agree with Wheelchair
You can become a millionaire off of blackjack. I'll go one step further and say that you would most likely have to have nerves of steel, a total disregard for heat, repeated ignoring of barrings, the mettle and bankroll to bet the table maximum without blinking and a method of advantage play stronger than counting. If an example of such a method does not occur to you, think for a moment about how a blackjack player could get the nickname 'Wheelchair'. Then realize there are many other methods beyond just that.
Hypothetically speaking, assume you could find a game in which you could get a 20% edge over the house through legal means (not impossible). Let's assume that the table maximum at this game is about $3000 (not unusual in the Las Vegas area). Let's assume you have the nerve to sit there and bet the table maximum in a heads up game until you get the boot. If you're lucky and your mug is not prominently featured in The Book, that could take an hour, maybe two, maybe several. If you got an entire hour's worth of play in before being 86'd/barred/arrested/sued/beaten to a pulp/shot/stabbed/hauled out to the desert and buried/all of the above that's .20 x $3000 x 200 = $120,000 (maybe more if you were playing multiple hands). Nine such sessions and you're expectation is to be a millionaire. For a more easily obtained 5%-10% edge, it would take longer, but still it is not an unrealistic goal. I could imagine other methods by which you could properly set your victim (the casino) up for a huge fall and get in several sessions before receiving the aforementioned 'boot'.
Eventually, advances in surveillance technology will make certain that your first such session will be your last...anywhere. So go out there and make millions before it is too late!
Also, it is worth diversifying your skills if you intend to make millions. Many methods of gambling are vulnerable to an insightful advantage player. Some, such as poker, don't even result in barrings.
But, ultimately, the best way to make millions off of blackjack (gambling) is to open your own casino.