Vaporizers blow or draw hot air through the weed @ 390*F and below..melting the trichs and producing vapor eliminating 90% of all the BS that smoke has in it.

Smoking weed your igniting the weed with your lighter(according to various links provided by the very handy Google.com a Bic flame burns at 1977* F.)

That high temperature ativates carsonages and tars ect. in the smoke from the weed