So......not a comparable situation then, ok.
but hey, if you want to argue with yourself about a slippery slope no one mentioned, who am i to stop you?
It seems you are having a good time with it, congrats.
edit : salty downvotes aren't a replacement for a coherent argument, they are however, entertaining.
Indeed, which is why it's an ever evolving suite of tests, as and when you come across problems and things that were missed, you add automated tests for them.
It's not magic, you only get out what you put in, but it is automated, which means that if you do a reasonable job you have a lot less to worry about from that particular issue in the future and now you have a much quicker way of checking for it.
Also agreed, and automated testing is a way to partially formalise that knowledge into something that can be checked quickly and deterministically (if you are doing it right).
As i said before it's not magic and it's not a replacement, it's more of an augmentation to relieve some of the cognitive burden.
As with any other approach, it also has it's downsides, there are ways to go about it that can be actively detrimental.
In my experience a well done (and maintained) automated suite is a boon to ongoing development.