I can see what you are saying, but not quite agree. Survival of the fittest is a natural process and when farmers breed their livestock using the best of the best to breed from, that the same thing is happening. Both are still the egg and sperm and their accompanying genes combining naturally. But gene splicing is a whole different thing. And is not natural in any way.
Without belaboring the point beyond what is appropriate, you need to know that there are indeed natural processes, i.e. ones that operate without man’s interference, mostly facilitated by viruses, that do indeed splice genes from one species into another.
I must state also for the record that I oppose, as should any thinking person, careless, reckless, or casual gene splicing.