I think it's okay to question anything. By question there I mean test or attempt to measure scientifically. That doesn't mean you're calling anyone a liar. It means you're trying to understand how the phenomenon works, why it works for some people and not others, and whether it might have interesting or useful applications.
If such investigation (voluntary for synesthetes of course) is not allowed, then you can't be surprised if people keep on expressing scepticism. Scepticism, about everything, is the foundation of good science.
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To soap or not to soap? Light hearted.
When did perimenopause become so popular?
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) and would rather say nothing, keeping my opinions to myself. After all, anyone who swore the world was flat would feel foolish now. 

