Having been a regular late person, I changed this by simply accepting the fact that young children need lots of time to get started in the morning. Everything takes twice as long - a simple instruction such as 'put your shoes on' can take 10 minutes to happen.
When I was nannying I would often arrive and the children were still in bed at 7.45, the lights out and the curtains drawn. Eventually I had to drive them in because the mother wouldn't get them up earlier (or to bed earlier as I found out).
I did recognise this as I did it myself. When they are younger you do everything for them and it's all quite quick but as they get independence it all takes twice as long but you need to allow them time otherwise you end up frazzled and shouty.
Partly with the help of flylady, the concept of planning the day before dawned on me. If I want them to be fully awake and functioning at 7.30 I need to wake them at 7.00 If I want them to be awake at 7.00 they need to go to bed a the latest at 9.00. The way I judge this is to check at weekends to see what time they naturally wake, and that is an estimate of the amount of sleep they really need.
Frazzled and shouty is possibly what these late parents try to avoid - and I can understand that, but it's not the right way to deal with it. If only I had flylady a few years earlier (or an alternative less churchy-midleamerica-1950s version) life would have been a lot easier.
It's not fair to let children be late for school, but it's equally not fair for them to feel frazzled and pushed so they just need lots of TIME.
In answer to the thread title, YABU if you are annoyed, because these people need a bit of pity and a bit of help. People do care, even though it doesn't appear that they do.