Its a bit like asking "why should I use javascript instead of php". Different computer languages are better for different things, like different blockchains are

Its a bit like asking "why should I use javascript instead of php". Different computer languages are better for different things, like different blockchains are better for different things. Ethereum comes with a built in state tracking machine and smart contracting language. It already has 98% of the protocol built... there's no need to start from 0 for blockstack. If the DNS/PKIs were on Ethereum, anyone could build applications that interact with it without altering the fundamental protocol. For example, a developer could build a decentralized auction or escrow system for domain names. They could do that without having to alter/adjust the existing blockstack protocol. Here is namecoin in 8 lines of serpent https://github.com/ethereum/serpent/blob/master/examples/namecoin.se https://github.com/ethereum/serpent/blob/master/examples/nam...