Where there are humans, there will always be human behavior. Steemit is no different unfortunately but I agree with you that it has the potential to change and stand out. "It can not be done" is a false statement, yes it can, it just needs the will to be done.
Memos in our wallets and those follow, unfollow junkies who hit those buttons a million times per minute just to get your attention would be history.
The system does allow it and sometimes I ask myself WHY. Is it because it can not be fixed? Nope. People are programming robots to walk, talk and dance. Rejecting any transaction from a blocked account seems simple when compared to that. Is it because people do not want to fix it for any reason? I would bet on this one. Wheater it is the lack of will, interest or just plain support for the spam behavior, when there will be people who can fix it and want to fix it, it will be fixed.