I think the preference against ids is covered over point #2 about specificity. id styles will always override class styles, so when you're trying to apply a class-based style guide to an element that's already been styled with an id, you end up having to use !important which just creates a similar specificity problem for someone else down the line.

Of course, you can still do this if you want to. To quote Chris Rock, "you can drive a car with your feet if you want to." But if you work on a large code base that lots of developers have touched, and lots of future developers will touch, you run into these issues all the time. And the bugs that come about can be tough to spot and to fix.

I agree with other poster.

For me it's a matter of doing things the same way so when I need to make an update to the code in a year it's intuitive.

"Be kind to your future self" is my motto.