[Dylan16807]

To perform constructive criticism you need to be able to say that something has flaws. Which is saying something negative.

[dijksterhuis]

Hmmmm, only if you assume it's a common possibility for X to be perfect from the outset.

Most things are imperfect. Assuming X is imperfect and has flaws isn't being negative, it's just being realistic.

Don't let perfect be the enemy of good enough pal.

[Dylan16807]

I'm not assuming that at all.

Constructive criticism involves being negative about the aspects that make something imperfect.

A realistic reaction to most things is a mixture of positive and negative.