They all have purpose. Maybe except Litcoin that has no use if Bitcoin will solve scaling problems.
There is a plenty of space for at least couple of coins and imho it is what we are going to see. Couple of blockchains with different purposes will share 90% of market share. There is a place for Bitcoin, Ethereum, Dash and couple others. Thing is all other cryptos need Bitcoin. If Bitcoin would fail, noone is going to trust in any other crypto for a long long time.