- Talking is an incomplete way capturing your thoughts. (Gets progressively worse with videos / phone calls / emails / telegrams ...). You will never capture all you're thinking in a few words. So IMO speaking your mind is essentially blurting what's floating on the top rather than actually speaking your mind. You probably can see how that can strain a conversation.

- Believe it or not, Communication is a 2 way problem: It doesn't matter even if you perfectly capture it, if the other party ain't listening. Or is only listening to cherry pick metaphors to rant on. Even if they are listening, the first few aggro sentences (or some that are sandwiched) can set them off - making them non-receptive to the rest. Again another reason people try to pick their words carefully so that they can put their best foot forward.

-A world where clairvoyance is the norm is where speaking your mind may make sense: Otherwise you are one of the few who is baring his soul every time while others are picking a time and place. Good or bad, I am sure you see this puts you at a great disadvantage.

- When bad news is delivered, we all process it differently. One of the common mechanics is attacking the messenger in some way or other OR trying to blame the messenger for delivering it badly. Again something to keep in mind when talking.

- Life is grey: If you want to define careful words as manipulation, that's polarizing the situation. In reality it could be manipulation or just plain old 'being careful'.

I am not going to be able to convince you in one post :) neither can I tell you how to live your life. These have been some of my observations that moved me from a 'speak your mind' person to a lot more 'reasonable' person model. So HTH!