I don't think you can consistently win at gambling. Even if you follow certain rules or have a betting strategy, the odds are still against you.
That's hard to reach, $50 - $100 is not a joke especially if you are going to gamble that online. We know that online systems are always in the favor of the house and even you play in real casino's you will have hard time to win against them. Gambling is not profitable for a longer term because it will just give you lose.
Let's assume that it is possible to a professional gambler. But not all the time it is going to be a great way to earn and just depend to it. Remember that the longer you are going to stay in a gambling site, you are prone in losing. If you want to use gambling for profitable activity, there's no other way on it but by investing.
I agree that a professional gambler may win in gambling in a long run. But these gambler lose too if luck does not favor them. I also agree that the longer we stay in gambling, the more prone we are in losing but we are more prone to winning too since it is a game of chance, anything can happen. Even investing in bankroll can give negative return. I have seen soem data here about house bankroll investment giving negative ROI.
It's proven that the longer we are going to stay at any gambling site the more chance of losing in the end. I think I know what thread you are saying about that negative return of investment. I have read it here somewhere too but I just forgot what's the exact thread.