In rough order of priority (highest to lowest):

a) I do not believe that it produces useful-quality results for almost any of my use cases (Even if other concerns were addressed, I don't want to generate buggy code I then have to debug).

b) I believe many if not necessarily all generative AI models were trained unethically on copyrighted data

c) I am worried about the legal & copyright implications of using the tool to produce work products for my employer

d) I am concerned about the societal implications of the tool's existence, and how it's producing sub-human-scale work for (nearly) free, thereby eroding the market for a lot of human-produced output.

e) I dislike the amplified volume of low-quality content online over the last few months.

f) I'm not a fan of OpenAI as a business or a potential monopoly

You really can't think of a reason? Or you don't want to think of a reason?

Same concept as blood money. To be dramatic, if the wrench was made with ore from a mine where your father worked, and he was killed and the ore was stolen, would you do business with the company that hired the mercenaries that killed him? Would you buy a wrench from them? if one fell into your hands, would you use it? It's just a wrench, after all, but you can see why somebody might have strong feelings about it, even if you ultimately disagree with them.