ive never heard a convincing argument for why it's necessarily a bad thing to "play god". it just seems like an oft repeated phrase that makes no sense to me and only survived because of some idea that we have no right to try and discern the true nature of the universe and then to control it in the pursuit of betterment of our capacities as a species.

Because a lot of "playing god" is thinly veiled authoritarianism -- the desire to control our fellows, out of our own egotism?

That's not what the term is generally used for.

Generally speaking, "playing god" is talked about as messing with nature and the things around us to better suit our needs. Genetic engineering, climate engineering, etc. "God" refers to the natural order of things and trying to change it.

"Playing God" is often used for activities where we're able to cause some change, have a hard time undoing our actions, and are unable see all possible consequences.

I wouldn't necessarily say "playing god", but we do vaccinate ourselves right? I mean I think the real issue is inflicting a change to a being that will become "Sentient" or "Conscious". When we genetically alter that which has potential for "life", do we know, beyond a doubt, that the change we inflict will be positive for the individual AND positive our species as a whole? If we cannot say for certain, then genetically altering sentient life (who have no choice), is not a good idea.