Some people seemed to think Katniss voted yes purely as ploy to assassinate someone? I guess her motivation wasn't made clear.

Really? I guess it's possible that was true and I missed it entirely, but yeah, I didn't get that at all. All I got was "SERIOUSLY????" (Because in the first book, she felt compassion even for Cato when the muttations were mangling him without killing him, and... and... sigh, again.)