I believe you should only give advice if you were asked for it. When I post a picture of one of my quilted projects I am sharing with friends. I don't ask for criticism because I know what I didn't do right. When I get complimentary comments I feel boosted up and feel more confident to try something new. If people started pointing out my flaws then I would be hurt and lose interest entirely and probably not share any more photos.
It is just like with kids. If they show you a picture they have been working on really hard and the first thing you do is criticize some part of it they would be devastated. I always point out what I like about their picture. " I like how you used that blue on the door of the house", etc.
As to saying nothing...I have mixed emotions about it. Yes, saying nothing isn't hurtful but when I've shared a photo of my project and nobody comments then I feel like nobody could find anything worthy to compliment.
I think this is kind of one of those no win situations. The best course of action is to be kind and thoughtful to everyone on this board no matter how inexperienced or masterful the quilter is.
Just my 2 cents........