I think the important question is what if you _do_ want to share that info, and other people are interested in hearing it, why aren't we talking about it?
BTW, I'm always willing to share, and the result is usually that people are eager to share with me (to varying degrees of precision, of course.) I don't have any issue with it because I never confuse my salary with my worth as a person. It's my worth to the company commingled with my ability to negotiate. When workers share salary information with each other, it smooths the last part out.
I'm not going to stop doing it until competing companies are required not to disclose the prices of their products to each other - and I see difficulties in the implementation of that:)