If you are worried about people stealing your idea, but it took 2 solid years to flesh out and is a relatively unrecognized problem, then you might relax knowing that even if you inspire someone else to pursue your vision, you will be their de facto leader and teacher, not their victim of theft.
Of course maybe you don’t mention the vision because you are tired of getting shot down. I’m not going to say that that somehow means your idea must be flawed; I think most people’s conception of big issues is flawed, but if the issue you are tackling is uncommon and complicated, and tempts ridicule, then you have an unholy triad of poor feedback. How do you personally form priorities if this is true?
All in all it sounds like you could use some quality, thoughtful feedback, or even just someone to listen intently, but uncritically to your conceptions.
As for the other, more generic problems: If you can inspire others with your vision and allow them to hold you accountable to make progress then motivation, passion and meaning can come much more easily.