This has a negative effect on humans doing their work with or without LLMs: curl shut down their bounty program, and GitHub just announced they're "restructuring" theirs. The author of this post also makes a case that HackerOne hasn't been honest about LLM training and use, either to hackers or to their own staff.
Automated triage can filter obvious spam, which was already fast and easy for humans to do. The hard part is independently reproducing a plausible finding and assessing its actual impact. If LLMs could already do that reliably, then the slop report problem wouldn't exist in the first place.
It sounds like a reason to try and build it than a reason to not build it.
I'd say instead that the problem is that a lot of people don't care anymore about the quality of the work being done, and LLMs are accelerating it. Bounty programs have shifted from ways for people to report security bugs to ways for people to try to make money.