I suppose there's infinite regress available to naysayers. If the system threatens failure and the failure warning system fails and the warning system failure alert fails, and the backup warning systems fail, and the back up warning system failure alarm fails, it could get bad if all that happened at once.
So add a backup warning system failure warning signal failure warning system that continuously tests itself. And a warning system in case the testing system stops testing itself. And three single new hires to monitor the little red blinking self-testing failure warning system light 24/7.
...and then the naysayers say "well, if it's so inherently safe, why does it need all these expensive warning systems???".
It's literally impossible to win this game; IMO the industry should just refuse to play. No more safety features, unless and until the design can be shown to be less safe than an equivalent non-nuclear generating technology.