I think Germans are more upset about how messy these things are than about the safety aspect. People just leave them wherever and occasionally some bored people do silly things with them like creating a huge pile of them or tossing them in canals, etc. They are not very stable and that means that even if they are parked properly, they can still fall over. Or people just kick them over. But mostly, stuff like this is a minor nuisance. Berlin is covered in graffiti; there's lots of vandalism, etc.. This just adds to that. I don't mind the chaos generally.
You also see people using them creatively. I regularly see people transporting furniture or even Christmas trees (last year) on these things for example. Or multiple people sharing a scooter. I find this hilarious. And there is a fair bit of abuse involving drunk people, kids doing stunts with them, etc.
But mostly, you just see people using them as intended. Berlin is a big place. You can walk for hours without leaving the inner city. Rush hour traffic is very congested and these things are perfect for getting around.
I kind of dislike using scooters myself; mostly because I don't like the lack of stability and danger level. But e-bikes are great and almost as easy to find. Most deadly accidents here in Berlin involve cars though. Stupidly and pointlessly large SUVs and trucks driven irresponsibly are usually involved. Right hand turns involving trucks crushing cyclists are very common here.