When I moved to Argentina, it took me a while to get used to bidets. But now that I'm used to them, I never use toilet paper voluntarily. It leaves your butt still dirty! As someone said, if you got poop on your arm, maybe while changing a diaper, would you wipe it off with a piece of paper and consider it clean? No, not if you're from the mainstream of any developed country. You would use water, soap, and maybe more…
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Having a separate system and jet of water seems like a lot more complexity with increased risk of splash. And the cleaning properties of dampened paper seem strictly better than a stream of water. Just like I wouldn't wipe off poo from my arm with dry paper, I also wouldn't just run my arm under water without also mechanically scrubbing it.
Obviously, most toilets without bidets don't have faucets close enough to reach from the toilet, so a bidet might be an improvement over the status quo. But it seems way easier to install a small faucet than a stand-alone bidet, and way less maintenance to have a small faucet than one of those built-in water jets for toilets.