Valid arguments on both sides here, but there a couple points to be made:
1) There is already a pretty robust backlash to GMO crops and animals. We've created, as one example, very specific chickens which grow bigger and faster. However, because of the increase in size, these animals cannot move. Thus they require constant antibiotics and hormones because they perennially sit in the waste mire of 50,000 other birds in the same vastly efficient building. It gives us bigger drumsticks and makes the packets cheaper sure, but we've known about problems like "superbug" antibiotic-resistant bacteria which could very well be a result of the constant ingestion of minute amounts of antibiotics in foods.
2) The complexity of both making the edits and the consequences grow with each discovery. Corrective surgery, supplemental tools, and other current inventions are not even on the same playing field as genetic modifications. I get the argument that we're not to "play God" seems overly simplistic, but we invested super weapons and power sources yet can't really seem to fully control those either. The zombie thesis is somewhat of a caricature, but then so is the Skynet thesis of Terminator. This quote struck me: "We are talking about heritable changes in the human genome that could be passed on potentially forever—we know of no proven safe way to reverse genetic modifications in people." Imagine a world where we introduce new a new virus or bacteria because of an unintended consequence.
3) You may not buy the Bernie-Sanders-style arguments for inequality, but this would surface even more with treatments initially available to the super rich and not available to us common folk. Imagine a world where an elite aristocracy lives 20-30 years longer than everyone else. You think that you have the ultimate nihilists and narcissists in politics now?
4) How about super soldiers? An almost super hero elite class? Yes, it's the stuff of B-rated scifi movies and video games, but as the aforementioned quote says, once we go there, it's very difficult to turn back. When we (collectively; humanity) invented glasses or surgery, that action was undone with the eventual death of the person. Now you're tweaking an entire line. I've always pondered over the question of does a murderer also kill the future line of the victim...well...does genetic modification forever change the future of the family of the line?
I don't know that I have the brainpower capable to answer a number of my rhetorical questions either way, which is precisely why slowing down makes sense. We all desire to increase the quality of life of loved ones who suffer tremendous burdens, but we also know this is a whole new world of consequences. I think that a serious review of where the Bible at least tangentially touches this topic (tower of Babel, Jesus words on the tower of Siloam, etc) yield that we do need to be cautious. He did say that our general sin capacity shortens our lifetimes. I'm not saying we should not challenged 65 or 85 years to go to 90 or 110, but we need to approach this very thoughtfully. Our Creator endowed us with the ability to create, but we cannot lose focus that it's his creation and our messing with his creations.