I assume you are talking about "drug markets."

Why would that be any different from a weapons market?

If either existed (in brick and motor or amazon style stores) I would frequent both regularly.

The difference, if I could put it in as mild a way as possible, is that it has yet to be conclusively demonstrated that safe, reliable access to weapons of known quality is a net positive to public health and safety.

Some of us see it as, drugs being something that one inflicts to oneself, while weaponry, assassination, terrorism and manufacture of pedophile pornography is, in contrast, inflicted to others by force.

Well yes, the last three in your list are terrible exactly because they harm others. That is what I said.

Weapons are like drugs, they don't necessarily hurt anyone unless you plan to invade my home or threaten me. Assassination implies that the sole goal is killing a target, buying a gun can be for protection, for a collection, for fun and hobby, for sustenance, ect.

gunbroker.com is a pretty decent online weapons market. I use it quite frequently (in full compliance with state and federal law).

If you're interested in this type of thing:

http://www.collectorsfirearms.com/ -- Mostly Military and Older Weaponry.

http://www.aimsurplus.com/default.aspx -- C&R, Military and Black Rifles

http://www.budsgunshop.com/catalog/index.php -- Modern Firearms from almost all medium and large manufactures

http://www.cdnninvestments.com/ -- Whole sale gun catolog.

http://www.slickguns.com is also a great "daily deals" site for guns and ammo.

Other good cheap vendors (in addition to the above) are http://www.jgsales.com and for ammo, http://www.ammoman.com/ and http://www.luckygunner.com/