Critical analysis and providing recommendations does not need to be negative. I see this every day -- engineers being emotional and negative. I recommend people keep their emotions out of it. You listen, you recommend, you support your position, and if the powers above you make a choice contrary to what your analysis determines is the best option, you calmly provide (and document in email or meeting minutes) the consequences of that choice. If the doors are closed and the decision locked in, recognize that you provided your recommendation, and now your job is to support the team, the company, in the implementation of the chosen path. That is professionalism.

If persistently executives make the wrong choices and persistently your documented recommendations and consequences have proven right, you will either be more closely listened to in the future, or this is a company that is not properly using a valuable, proven resource and it is time to find other employment.