Originally Posted by Francesca Knowles
Because it's the polite thing to do.
Besides, I always have Sister Mary Agnes of The Cross from 5th grade whispering in my ear:
"Never say anything that you don't want to be held responsible for."
An alias would never pass muster with such a strict mentor.
While I agree in principle, in practice for most folks, it's about privacy rather than politeness. As an example, prospective employers routinely google applicants names. Is it really their business to know that you may like to camp, post to a vegan food site, or prefer country music to classical? What if they found a picture of you holding a beer around a campfire? What assumptions might they draw based on your internet presence that could impact your future employment?
IMHO putting your name, e-mail address or phone number out there is just tempting fate. We can still be polite in the absence of full disclosure of personal info. Think of it as being on a first name basis (only)