Honesty Verses Opinion
Being honest about your thoughts, feelings and opinions is important. It allows you to be true to yourself and those around you.
Being truthful and factual in what you say is just as important, but is completely different to an opinion - even a truthful opinion.
I believe in truth and tact, and being aware of the difference between truth and opinion. And as much as I'm 'for' honesty - I think some people often fire off opinions under the guise of truths. These tend to be the 'brutally honest' people. In my opinion, 'brutally honest' normally isn't real honesty at all - just someone who's highly opinionated making excuses for being so.
Keeping you mouth shut about an opinion isn't lying or dishonest, and is a part of being tactful and caring about the feelings of others. This is just as important and honesty.