Google is probably trying to get around the cardinal rule of network security: you can't trust the client.
Their RCS client probably doesn't make sending a huge volume of messages (i.e. spam) easy, and more automation is possible with root. Yes, it's stupid, but it's not completely without purpose.
What's really bizarre is that Google had the chance to be a dominant player in messaging when they made Hangouts the default SMS client on Android. Instead, they backpedaled and let Hangouts wither into obscurity. I'm mostly glad they screwed that up, but also puzzled.
I want to say research on the subject has been inconclusive overall. I'd certainly update my view given convincing evidence that fictional images lead to abuse of real children.
Of course, none of that has anything to do with the non-explicit video linked elsewhere in this thread of an adult woman using the toilet.
This may be controversial, but I don't care what kind of AI-generated images people create as long as it's obvious they're not reality. Where I worry is the creation of believable false narratives, from explicit deepfakes of real people to completely fictional newsworthy events.
Necessary is a matter of perspective, and what it is you need your device to do. Mine is that if you don't have root (or equivalent) on a computer, you don't really own it. That's a philosophical point more than a practical one - I'd want root even if I didn't currently have a use for it.
Practically, here are some things I use root for in 2023:
Advanced charge controller - limit battery charge to extend service life. Some devices have a built-in option now, but it's usually only a single switch for 85%. I usually set it to 60%.
Backup of apps with their data (Neo Backup), to install onto another device or after a factory reset - I don't think there's a way to do anything like this without root.
Mounting remote devices for access by arbitrary apps using EasySSHFS - I don't think there's a good equivalent.
Accessing exfat format external drives, like the SD cards in my camera using MiXPlorer's built-in filesystem drivers. Android is an asshole for not supporting more filesystems. It's Linux; the support already exists.
Hosts file ad blocking - DNS ad blocking is a viable alternative now.
If something blocks me from using it with root, I'll give it a 1-star review on Google Play and probably not use it even if I can get around the blocking. If my bank starts using more effective blocking, I will probably change banks.
