As with all systems, schemes, and methods, when Martingaling, you create a spread, or an outside limit on how much you're willing to lose at one sitting, based on the amount you walked in the door with.
It doesn't create vast wealth, or fast wealth, but it can be used successfully for short periods. If you don't believe that, buy six or eight decks of cards, some chips at the local toy store, and practice alone with one other person, or with three or four friends at home. If you stay with it, you'll win X amount every hand you play until you leave the table, or until the cards go against you.
Bet $10. If you lose, bet $20 the next hand. Keep doubling until you win, and then go back to your original $10 bet. On occasion, your loss will exceed your pocket money, so you need a cut-off point, just as you would with any other device. You may want to stop after a 1 - 4 spread, or when your bet reaches $80, or 1 - 5 at $160. You may also not wish to double-down, or split pairs, at that point until you get back on track. After making back 1 to 1-1/2 times your seed money, you may want to move on. You won't make a living betting this way, but it pays for a nice meal or the gas for the trip.
The fanatical opposition to Martingaling is ridiculous.