This thread is closest to what I was thinking when I read your poll. I wondered at first why you would ask the question. But that's because I was interpreting 'opinion' to mean something like 'thoughts and interprations about things that are open to interpretation'. Where in fact you are more talking about belief systems, and the use of the phrase to shut down debate.

To take a trivial example, I am of the opinion that The Apprentic is worth an hour-and-a-half or so of my time once a week while it's on, and I think the world would be a better place if Big Brother were not on at all. Others are equally entitled to hold their own opinions about various reality TV prgrammes; and that entitlement places no duty on anyone else, as far as I can see.

But use of the phrase to shut down debate on important matters -- in particular, matters where there is objective truth to be found -- should definitely be discouraged.