We've been manipulating genotypes to effect changes in phenotypes for quite a while. How's that?
Cross breeding and induced mutation mimic processes that occur in nature and differ only quantitively, say, in the amount of radioactive bombardment of genetic material. Gene splicing, especially between species, is entirely new and qualitatively different.
All I am saying is that it is different. It, if history is a guide, may be a long time before we know if it is a good or bad thing. I am always leery unintended consequences.