I feel even in balls to the walls aggro it's a sideboard card for the mirror match at best.
besides that I would rather another threat or shock.
You can of course make a good Rakdos aggro deck without it. I've played 7 of the 10 decks in the current deckbuilders challenge so far, and they've all been pretty good with or without Alms in their particular lists. In the lists that do run it, you can check my recaps in the thread to see how often that card wins games (might surprise some peeps who think it's bad). I also have gameplay video if peeps think I'm BSing.
I personally prefer it to other threats or shocks, etc in my build. It has advantages over creature threats by being faster than a non-hastey creature. Hastey creatures are going to cost you 3 mana at least, but you can madness Alms for 1 (getting additional benefits via the discard source - giving evasion to Dragoon, making something unblockable through Key, drawing cards with Copter, casting an undercosted 4/3 beatstick, etc) and don't need to worry about spot removal or blockers keeping damage from getting through. In balls to the wall aggro all this matters cause you're trying to win THIS turn.
In regard to something like Shock - similarly costed to Alms madness - 3d kills faster than 2d, and the card effectively reads 'you win this mirror match'.