You can purchase loose produce through a self checkout, I do it nearly every time I do a food shop.
Regarding your second point, I get that and think there should always be a couple of manned tills, but these days the priority should rightly be self checkouts, those of us who work full time and have busy family lives want to be in and out of a supermarket as quickly as possible.
I find there is more room for error with manned checkouts too, at least with self checkouts I can keep an eye on what is happening, I can't accidently scan something twice and I know I'm scanning the right barcode if something has a yellow reduced sticker on, both of which I've had to point out when I've used a manned checkout recently.