I just can't see how people in a free market would choose altcoins over bitcoins. If given the chance of being paid an amount in BTC or ATC, I'd definitely prefer the BTC, which will store value better than the ever-expanding ATC. This preference for bitcoins would make altcoins fail.
Think the situation other way around. The one being paid prefers bitcoins, but the one paying prefers altcoins. If this makes a currency fail, same could be applied to bitcoins, just the inverse.