The ones who need them are actually the minority of users. These however can still be edited in designer mode as mentioned by Matt.
I would say, with regards CSS being harmless, and people being able to restore, you are referring to yourself as a user here, and not the majority. While we do provide tools to revert templates, and even to check on default themes without doing that, people tend to post a topic/ticket on these things in the first instance. Something being harmless really depends on context. What is harmless to you, may be harmless to others. One person missing all the CSS on the front end and posting a ticket, is another persons "Its probably cache, so I cleared that and it was fixed in a second".