Mathematics and common sense in general speak differently. In the short term with luck on your side you may be able to profit, but the reality is that there are ridiculous patches of bad luck (ie. doog reported some guy got hit with 31 losses in a row running martingale). The only way to profit with martingale is if both:
a) you have infinite money (why are you gambling then - for the lols?)
b) there is no max house bet (which there always is otherwise you'd be able to bankrupt the casino very easily if you got lucky)
So basically the house edge will always get you if you play long enough (or just have shitty luck).