Why is it morally reprehensible to make human hybrids? Is it no more reprehensible than all modification (including selective breeding) we do all the time? Abo

Why is it morally reprehensible to make human hybrids? Is it no more reprehensible than all modification (including selective breeding) we do all the time? About the only bad thing I can see is the rationale "because we can". That is not a good enough reason.