Every time someone asks "Why do we need [altcoin] when we have bitcoin?" I'm reminded of the disturbing bitcoin-related proposals like blacklisting. If bitcoin goes down that road, and [altcoin] doesn't, I can see a lot more people making the switch.
As of now, none of the altcoins implement protocols that would protect them from such blacklists, so any sort of safe haven would only be temporary or otherwise imagined.