Good question, shminux. Another way of putting it: If cows and chickens don't count, why have any animal protection laws? Their guiding principle usually is the avoidance of unnecessary animal suffering. And if we agree that eating animals (1) causes animal suffering and is (2) unnecessary because we can have animal-free foods that are equally tasty, then the guiding principle of the agreed upon animal protection laws actually already implies that we should stop farming chickens and cows.

Note also that the Three Rs – which guide animal testing in many countries – reaffirm the above principle. Many believe it should be illegal to cause any animal suffering if it's unnecessary, i.e. if there is an acceptable alternative for the purpose. (And if there is not, we are under an obligation to try and create one.) If we take seriously what almost everybody accepts when it comes to animal testing, we should stop farming animals.

It seems that the arguments for according non-human animals a very important place in our practical ethics can only be blocked by claiming that they/their suffering matters zero. If it matters just a little, the aggregate animal suffering is still likely to matter a lot. And even if we are inclined to believe that it matters zero, we should retain some non-negligible uncertainty, at least if our view (like Jeff's) is based on the claim that some not-really-understood (!) combination of suffering with self-awareness, intelligence or other preferences is what makes for moral badness. If we are wrong on this one, the consequences will be catastrophic. We should take this into account.