Though you could simply report them, in some cases it would be more practical just to block them, especially in cases where they are not breaking any defined rules. Also, there is an option to block members from PMs, so wouldn't it make sense to be able to block from profile feed as well?
Look here. You can now control who can view your profile (Everyone, Registered Users, or just Friends), who can view your contact information (Everyone, Registered Users, or just Friends), and who can comment on your profile feed (Registered Users, Friends, or people who are allowed to message you). So if you want to block someone from commenting on your profile, you can choose the last option and then just block them from sending you PMs.