I can't say that I agree.
I've actually been in a real world analog to the attacked by possessed house cats scenario. I needed to take one of my cats to the vet and she objected. My other cat reacted aggressively to this situation and he attempted to attack her. I was holding her out of his reach while he was swatting at me trying to get at her, all the while she was trying to climb me to get away from him (and also possibly to get away from me). I had to hop on one foot while using my other foot to fend him off, in order to back him into the bathroom so I could shut the door and get her into the carrier so I could get her to stop trying to climb me. Needless to say, I was covered in bloody scratches from my chin, down my torso, as well as my legs and foot (yes, just the one foot, the one I'd been hopping on was whole and unbloodied).
Then I packed her in the car and took her to the vet. I didn't even have time to try to stop the bleeding, as the whole fiasco had us running late. At the vet's I could see them staring at me but they were polite enough not to ask. When I got home and stopped the last of the bleeding (it had mostly scabbed by then) my wife (who was my gf at the time) opined that I might want to go to the hospital, but I declined. And sure enough, while you can still see the lines in the summer when I'm a bit tan, no real harm came of it. It hurt quite a bit, but at no point was I in any real danger of harm.
Am I some 007 badass? As much as I'd love to believe that the case, I'm a 40 year old code monkey who sits behind a desk all day (although at the time this happened I was in my 30s). Realistically, I'm an average joe. I believe that if I can be scratched dozens of times without being significantly worse for wear, any average person could.
I imagine that there's some critical accumulation of cat scratches that could equate to real harm that could cause disability, but I would guess that it would be in the many hundreds or even thousands of scratches.
You could give commoners 500 HP so that they could withstand a "realistic" number of cat scratches. However, then you would need to adjust all other damage to account for this. It doesn't make sense for a longsword to deal 1d8 damage if a peasant has 500 HP after all.
Obviously, it's your game, so do whatever makes you and yours happy. I just don't think that increasing HP addresses the issue, even if you make cats deal non-lethal damage.