When one presents an opinion as "fact" therein lay the roots of defamation litigation ... and our litigious society just jumps at the opportunity to file a lawsuit anymore — all in the name of that punitive damage assessment by which so many wish to hit "easy street" allowing some schmoe to support them in perpetuity for their alleged casting of aspersions.
If you have an opinion you are not alone. We pretty much all do. But much like your nose and your butt which you likewise have they may all smell. You just have to exercise caution in how you state your opinions because of the consequences of claiming something as being factual when it isn't.
Remember, it's not character defamation when it's true. If you cannot ensure the veracity of your words it is far better to tread softly and with discretion around certain subjects when in public. To thine own self be true — but cover your ass as well.
The Art of Extracting Blood from a Turnip