From my laymans POV, DNA is just a shit ton of variables in a very complex code that interact with each other. No single point just does a single thing. They all interact with each other. No different than changing a variable in one piece of code and having it create a bug in another that was previously working.
For me, the real scary part is altering something, which inadvertently changes something else that isn't quite as obvious and visible or noticeable. Something that might not present itself until whatever organism it is reaches maturity, or beyond. Something like "everybody will get Alzheimers by age 50" where it takes 50 years to even discover it. And in the meantime, they thought whatever they originally tweaked was a success and made other tweaks during those 50 years thinking everything was just fine.
For me, the real scary part is altering something, which inadvertently changes something else that isn't quite as obvious and visible or noticeable. Something that might not present itself until whatever organism it is reaches maturity, or beyond. Something like "everybody will get Alzheimers by age 50" where it takes 50 years to even discover it. And in the meantime, they thought whatever they originally tweaked was a success and made other tweaks during those 50 years thinking everything was just fine.