[TylerE]

> Supposing that sidechains can be mined simultaneously with the bitcoin at no additional cost

Which is obviously not true. Extra storage and bandwidth at the very least.

[fryguy]

Hash rate is independent from bandwidth/storage. Assuming you can do N hashes/s, you can still do N hashes/s with merged mining of multiple sidecoins.

Also, presumably any bandwidth incurred by a sidecoin would have been incurred by bitcoin if the sidecoin didn't exist, so total bandwidth/storage would be similar.