Somebody is shining you on, or doesn't know what he's talking about. A polarizing filter is one of the most common accessories in photography. I own at least half a dozen of them. One of the things they do is reduce or eliminate glare from reflections on glass, water, etc. You rotate the filter to control the effect. A polarizing filter for a scope would be designed for sniper use (who else shoots through windows), but there's no restriction on owning one.
You can Google around for a scientific explanation of exactly what a polarizer does to light waves and what its practical uses are. It's pretty simple if you passed physics in high school.
Don't use a polarizing filter with polaroid sunglasses. If the two of them get at 90 degrees to each other, they will cut off the light completely and you won't see anything at all through the scope. I once made the mistake of having my prescription shades polarized, and quickly discovered I could no longer use the polarizer on my camera! That was an expensive mistake as I have a complex, expensive prescription.