The hot-or-not craze at least had the decency to allow you to opt-in for judgment.
You'd also have fewer profiles, giving the chance for more votes for top hotties.
And you'd have a better group of people to market dating offers to... :-)
Would an opt-out be satisfactory?
Overall, I prefer not to see 1-word answers at the top of any comment chain-- they're upvote bait that are typical of sites that are a lot less useful than HN. They certainly don't promote good discussion!
For example, the comment from thesethings helps us understand better the position: http://news.ycombinator.com/item?id=603676
Look, I put my picture onto my Twitter profile for use and recognition by the broader community. So people know who I am. I don't put it out there to be part of some (in my opinion) derivative, uninspired and shallow excuse for "entertainment".
No one puts their pictures on Twitter up for that reason.
So, if you're going to build something in a race to the bottom, at least have the common decency to tell me that you're lifting my profile picture and give me the option of getting the hell out of there. And don't use my picture until you have my permission.
Anything else is just jackassery.
The site works well, I'm sure there's an audience for it.
Plus, the nature of your site, unlike say favrd (which is not opt-out, but you'd only appear there if people loved your tweet, and would never appear there if they didn't) is something people naturally feel self-conscious about, appearance and attractiveness.
I do think the functionality and design is really nice though, you did a great job.