All animals are not equal. I find it much more difficult to hit an innocent puppy than step on a ladybug.
Saletan has written a post on that in slate
GAP is scientifically honest. And science doesn't show mental parity between great apes and human adults. What it shows, as the group's president acknowledges, is that great apes "experience an emotional and intellectual conscience similar to that of human children." Accordingly, the Spanish proposal doesn't treat apes like you or me. It treats them like "humans of limited capacity, such as children or those who are mentally incompetent and are afforded guardians or caretakers to represent their interests.
(Apes) enjoy a rich emotional and cultural existence in which they experience emotions such as fear, anxiety and happiness. They share the intellectual capacity to create and use tools, learn and teach other languages. They remember their past and plan for their future. It is in recognition of these and other morally significant qualities that the Great Ape Project was founded.
But there is a problem. Once you open the door of rights to non-humans, then you have to start judging ALL living beings on a spectrum, where the question of rights becomes a QUANTITATIVE question rather than a BINARY choice between all rights and no rights. What happens when the rights of very intelligent animals conflicts with that of very unintelligent humans? Whose rights win out? For example, would it be justified to destroy an ape habitat to make way for a facility to house the mentally ill?
Should rights be proportional to intellectual capacity? It would be difficult to argue otherwise if apes were granted rights but mice weren't.
In that case, would rights be apportioned more to racial groups that are more intelligent?
Disturbing questions. Only more justification for the singularity.