I also don't think that playing against bots is bad. However, playing blitz or bullet in general (against bots, humans, aliens or whatever) isn't going to improve your game. Playing slower games and analyzing them will.
The same is true for Puzzle Rush. Rush is just for fun, but solving puzzles slowly (trying for 100% accuracy, never mind the time) is great to improve your game.
I like playing bots but I know that's no bueno....So I don't give a whoo ha about blitz so I use as it a replacement to playing bots that don't play like humans. I think not caring is why people like playing bots because there is no pressure. You can think all you want and if you lose big deal.
I slightly disagree that playing bots is bad, because the better ones play normally for a while at least, and I just think it's good repetition and because they play the same stuff in the openings at least. I guess that's what I'm saying is blitz is better for opening work but bots work. The problem with begginer blitz is the middle game tactics. The tactical forcing moves just aren't natural to us yet. But we'll get there if we choose to....It really is a choice to get better for most people.