Consider 2 miners. One hopper and one non-hopper. Imagine that both of them have 1GH/s. It takes both of them 4s to generate a share. Now one goes gives that share to a pool which offers a lot for it, but the other gives that share to a pool which offers less. What is immoral in that?
As I explained, pool hopping breaches the implied covenant of good faith and fair dealing between miners.
And really, the pool does not offer less for a share because of hoppers. It there were no hoppers that pool would still offer less for that share.
That is incorrect. The pool really does offer less for a share because of hoppers.
The expected payout per share is based on how many shares have already been accumulated towards the current block. The lower that number, the higher the payout per share. Now, consider a pool's hash rate. The more pool hoppers the pool has, the more the pool's hash rate will go up when there are fewer shares accumulated and will go down when there are more shares. The share count resets to zero when the pool finds a block, which is determined only by the average hashing power. So more pool hoppers means more of that average hashing power comes out at low share counts and less at high counts. This means the pool spends more time at high share counts than it does at low share counts.
For a non-hopping miner, the average payout per block is solely depending on the average share count. This goes up with more pool hoppers because the hash rate goes down when the share count is high, leading to more time spent at the higher count.
I do see a lot of defense of pool hoppers based on misunderstandings of the mathematics. The analogy to coal miners sharing a vein is apt. The more mine hoppers in this case, the less time the miners spend mining a vein (because there are more people mining then, so it goes faster) and the more time the miners spend trying to expose a new vein (because there are fewer people mining then).