In a meeting or a social gathering, people will expect you to contribute to the discussion. In situations like these, it is very important to realize that even if your opinions might be honest and true, they could hurt the sentiments of a lot of people who might not be agreeing to these opinions of yours. Even if what you mentioned was correct, some might feel offended by your direct statements.
In these cases, it is always advisable to use a diplomatic tone. There is nothing wrong for two completely different persons to disagree on a point. But the objective should always be to put your contradicting thoughts in such a way that the listeners judge the sentence, and not you. This art is called agreeably disagreeing or constructive disagreeing.
In a constructive disagreement, which is bound to happen when a meeting of talented and dynamic people is held, the idea is to make sure that personal egos and prejudices don't overwhelm the discussion.
The focus of every agreement or disagreement should be to bring improvement and greater success, and on finding a solution and not settling personal scores or gaining one-upmanship. Mutual respect should be there for all participating members, even if their views could be clashing with yours.