Okay, Dunning-Kreuger confirmed. Not that I'd suggest telling him that.
He's probably referring to the second law of thermodynamics, which states that the total entropy
of an isolated system will increase over time, or at best remain constant. But Earth is not an isolated system; we get energy from the sun, for example, which constantly increases the amount of energy available to do work on Earth.
However, there is no such thing as "genetic entropy". For all practical purposes, genomes don't even notice entropy. By the same token, entropy has nothing to do with the amount of complexity in a system, only the amount of energy available to it. It's true that limiting available energy limits complexity, due to not having anything available to do the work needed to build it - but by the same token, having too much energy also limits complexity. It's kind of like trying to do something while someone is spraying a firehose at you.
In point of fact, genetic mutations usually happen due to high
-energy particles (such as x-rays and gamma rays). The best way to visualize their effect is like imagining a bullet hitting something - it's the sudden increase of energy that does the damage. By comparison, the effects of entropy would only take effect over untold billions of years.
As for the rest of it, his idea that a "perfect genome" would have no problems with interbreeding displays an appalling ignorance of the realities of biology. I don't care how 'perfect' someone's genome is (and what exactly is a "perfect genome", for that matter?), it can't ignore the effects of genetic drift, which would have pretty much ended the human race before it ever had a chance if it had started with only two humans.
I will say that he's more or less right about how most mutations have either a trivial effect or none at all, and thus natural selection takes no notice of them. But that is no reason to assume that these small mutations represent any 'degradation' of the human genome, especially when the major premise of that assumption - that entropy reduces complexity - is demonstrably false. Lack of energy preserves
complexity - thus why we can preserve things by freezing them or encasing them in nitrogen gas, among other things. Not to mention that eventually, even small mutations will add up to something that has a non-trivial effect, at which point natural selection will take notice of them.