It's not allowed as a 'default feature' , specially those new people who can steal works, resubmit them cosiderating as his own, then blocks the original owner making sure he don't flag the submission ( The reason why we have support section ).
Other than that, more reasons why blocker should be an unlock in the posts below...
I'm generally in favor of such an unlock existing, since it could save you from the trouble of having to report harrassers individually.
However, I'm also content with the fact that it's buyable with points instead of being available for free, since that'd make it prone to much abuse by members who feel that they're being harrassed by everyone and everything when they're not.
Way I see it, you save points to unlock the blocker. In the meantime whatever trouble needs settling just contact and work it out with a moderator. From what I hear, that's a major bullet point on their job description. That builds a relationship with site staff and familiarizes yourself with site tools. Its not tattling if you have valid reason. Still don't overuse that.
Then when you can save up for the points you unlock it. Really blocking should be considered a last resort, not a primary solution. If someones being a jackass they should get smacked on the wrist until they straighten up, and if they don't, the boot. When someone blocks them, its sometimes simply closing the lid on a bomb, they'll probably move to another user to be an ass to.
Most problems I've had were settled with a moderator, and future problems with those users prevented with the blocker. I've had one guy lash out at me for giving him an honest rating he didn't appreciate. Went to the extent of "attacking" by giving 1 ratings to everything I submitted. A moderator got to that before I even noticed, and removed the ratings. So to prevent any future interaction I blocked him and avoid him and his submissions on my own terms.
You should really have a good reason to block someone and when you can block people easily, it leads to more internal conflict.