Good news, it doesn't block! It just puts a red mark next to their name, so you can put less effort into that comment, if you choose.

And, it's social. If someone you've marked green is also using this, and they marks someone green that you have marked red, then you'll see a contested red-green next to them, which is a good "you should probably reconsider" indicator.

A good idea, but I lament the downfall of Slashdot.

They had the same sort of system. Friends of foes, they calldd it.