Like how deadly they are, microplastics and pollution from tire/road wear, noise in residential areas, the huge waste of area, expensive upkeep of infrastructure, how they make cities less inhabitable etc etc.
Everyone says they would love to live in a walkable city, but for some reason, at least in the US, the biggest gainers in population over the recent decades have been all automobile-centric cities (which are probably more accurately described as a large patchwork of suburbs). NYC would have shrunk due to out-migration to other places if it wasn't for foreign in-migration[0]. Chicago lost people 15 out of the last 20 years[1].
[0]: https://www.nyc.gov/assets/planning/download/pdf/about/dcp-p...
[1]: https://www.chicagotribune.com/news/ct-met-census-chicago-me...
Well the US is never a good example for that, because the US notoriously completely screwed up their city planning w.r.t. cars.
You need to look at examples of cities that were not built around the individual cars to check whether that's possible or not, and whether people like it better or not.
The parts of Chicago you'd think about when you think "walkable cities" are thriving.