Perhaps if people are made to feel their opinions are worthless, they will respond by developing opinions that are less subject to that characterization. People whose contributions to the process are not reasonable and thoughtful damage the process by their participation, and coddling them by insisting on equal valuation of their opinions is counterproductive.
The thing is that the vast majority of people do have good opinions and write them in good faith with the best of the project in mind. You may not always agree with them, and surely not all opinions are equally insightful, but that's a different matter.
What hurts the project is that some people choose to be dismissive of others and sometimes plain offencive.
Oleg