I don't think they are nearly as bad as cars from a waste perspective, even if they are short lived, it takes quite a few of them to make one car worth of (e)trash.
If they weren't allowed on sidewalks and parked in (repurposed) car spaces I'd be fine with them.
Cars don't get thrown in rivers do often.
They've been pulling at least one a month out of my local river for the past 8 years or so.