It seems to me that many people exhibit this tendency and I am looking for a good word to describe them. They love providing feedback but in a passive-aggressive way. They love giving their two cents but stop short of actually putting themselves in the position of having to commit to an answer.
For example, I might write the following sentence:
On the English Language & Usage stack exchange, certain ________ people are more ready to populate the comment section than they are to provide answers.