ALL OPINIONS ARE NOT EQUAL.
An opinion that has been well thought out and researched,
is worth more than one that has not.
One example of two opinions which are not equal:
The opinion that the Earth is flat,
the opinion that the Earth is round.
Some opinions have much more proof behind them than others. Not all opinions should be held in the same level of respect. Look and ask for sources. Check those sources' credibility. Just because a person holds something as their opinion, does not mean it cannot or should not be questioned.
Opinions can be important.
Opinions are used by people to decide who and what they will vote for, what products they will or will not buy, what activities they will or will not do. A change in popular opinion can change an aspect of the world.
Do consider, however, if an opinion really is important enough to be questioned. If it is over which band or TV show is more pleasing to the opinion-holder, such an opinion is not likely important enough for anyone other than the opinion-holder to question.