This is the classic response to criticism of open source projects. It tends to drive away people who otherwise might have been convinced to help.
Unfortunately, while the comment above was rather acerbic and in poor taste, the idea that you should keep your comments to yourself unless you can directly help the situation is not in itself helpful.
For instance, I can point out that you might have a scary looking mole on your neck, and should probably go see a dermatologist, without actually being a dermatologist.
Saying a UI is difficult to use, doesn't adhere to convention, &c, even saying it may not look sexy/ggod/æsthetic for a reason is one thing. Chiding the author for a "Win95" look is just childish.
Unfortunately, while the comment above was rather acerbic and in poor taste, the idea that you should keep your comments to yourself unless you can directly help the situation is not in itself helpful.
For instance, I can point out that you might have a scary looking mole on your neck, and should probably go see a dermatologist, without actually being a dermatologist.