A lot intelligent people are rather confused about criticism, especially in our “free-speech” free-for-all internet age. When they say “constructive criticisms are welcome” they mostly mean “bitching and complaints not welcome”. Rarely do people actually mean that “criticism without suggestion of possible solutions are not welcome” or “impolite criticism not welcome”.
Such discernment is important. Wanton bitching as internet-using geeks are used to is not criticism of any form.
People can be respected and make a living out of criticisms, called critics, but not bitching. And when one really value opinions, you often want criticism without qualifications. Just be happy that valuable criticisms may come to you free from the experts in the public. The instant you qualify what kind of feedback are welcome, your feedback is compromised. (this is particularly so for political or controversial subjects)
One easy way for many of the unix geekers to see this is the cryptology industry.
If a person really desires valuable criticisms that are polite or with solutions or “constructive” (whatever that means), one usually has to pay.