A big problem is that vibe-coded stuff tends to be much harder to maintain as the 'author' diesn't actually know how it works, and the code was not built for humans to understand. That's not a problem that's unique to LLM generated code, but it is common place in code that is, so "was this generated by LLM/AI" becomes a useful proxy question for "is thus codebase likely to be harder to maintain, and thus be less likely to be maintained well?"

There's also the sociatal level costs of using these models to consider. At present, they use significant amounts of power and cooling, both of which lead to adverse environmental effects. It serms quite appropriate to ask if a project using them, and to make the choice to avoid those that are, out of principal as well as technical concern.

You can audit the code but something like:

The rate of commits and new features seems rather high for a single person working by themselves

Is a huge problem in itself IMO. It implies there's no real human oversight of the project.

Not everyone can read code.

From those who can, not all have the same knowledge that may be required to read this specific tool.

From those who can, not all have the time or willingness to do so.

Not wanting to use something that had AI input is just as valid as not wanting to use a specific tool, programming language, operative system, or browser, because it goes against your principles.

Software always had bugs long before vibe coding was a thing, we all understand that.

Many of us are on Lemmy because we don't want to contribute to Reddit.

OP is not trying to convince you to not use tools that AI never contributed to, no need to try to convince him to use tools that AI may have potentially heavily contributed to.