I think the majority of people bitching as if the sky is falling because of scooters are people who live in the burbs and only go downtown a couple times a year... and are mostly repeating what they hear their neighbors say (who also barely ever go downtown).
I work downtown and see the reality of it every day. Between my building and the one across the street there are typically ~40 scooters parked along the sidewalk- mostly orderly enough although there's always a stray or two that have been blown over by the wind or just left on unstable ground and fallen over. The city painted designated areas for scooter parking where I work on 2nd street a month or so ago and most people leave them within those boundaries.
As for riders acting recklessly, on regular days it's not any different than cyclists have always been downtown. With SXSW there are many more scooters and people downtown than the rest of the year typically and it is certainly pushing some limits, but overall it's not nearly as bad as some here are making it out to be.
My co-workers and I use them occasionally to go to lunch or get drinks somewhere a little farther than our immediate area (2nd Street District), and like Mycoxaphloppin said, it's much quicker and better than walking when it's 98 degrees outside if you're only going 6-10 blocks away or something similar where taking an Uber makes little sense.