Hi there, while we hope you enjoy browsing through the site, there's a lot more you can do if you register. The process is easy and you can use your Google, Facebook, or Twitter account to make it even faster. Some perks of joining include:
Create your own topics, participate in existing discussions, and vote in polls
Show off your creations, stories, art, music, and movies and play member and staff-run games
Enter contests to win free LEGO sets and other prizes, and vote to decide the winners
Participate in raffles, including exclusive raffles for new members, and win free LEGO sets
Send private messages to other members
Organize with other members to attend or send your MOCs to LEGO fan events all over the world
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.