I also think the concept that you have to open a critique with a positive statement is kind of juvenile.

Critique, by definition means people want the weaknesses identified. Yes, you can be totally ruthless, or you can be more polite, but it doesn't change the content. It is nice to comment on the positive attributes as well...but if all you can think of is: "nice tail"...just don't bother. Highlight the weaknesses and then comment on how nice the PHOTOS are or something, don't blow smoke up someone's ass...that's not being "nice" or "respectful"...that's lying.