As with most of these things, the first thing that springs to mind is "unnatural." It is a violation of the natural law. And we all know from the old Frankenstein movies that violating the natural law is not a good idea.
The second thing that springs to mind is that it's better not to let the genie out of the bottle. Once you pop the cork, you will find it very difficult to persuade the genie to go back in again. Or, to put this in less metaphorical terms, once the research has been done, the funds invested, the startup companies hired their researchers, secretaries, and janitors, it will be a great deal more difficult to change your mind.
The best time to stop it is right now, before it starts. But regretably there will always be plenty of people around who will want to do it because, like bill clinton, "I can." Still, it would be far easier to stop it now than to wait until after it gets out of the bottle.
Once you get started sliding down this slope, a later step will be to get the embryo to come to term and be born. Now we will have to answer the question: at what percentage of human DNA will the resulting organism be defined as legally "human" with human rights?
I can see some governments becoming interested in the creation of a race of beings with limited intelligence, docile and submissive temperment, and non-human appearance (so that many humans will not consider them to be worthy of full human rights). For what happens next, the original "Planet of the Apes" film series from the 1960's/70's comes to mind