I personally believe that unless a man has a contractible disease or is trying to get a woman pregnant, all sperm and semen should be swallowed voluntarily by willing cum sluts. I know if there wasn't a social and religious stigma against being a cum slut, thousands of gallons of sperm would be swallowed every day.
If everyone felt that sperm and semen should be respected and honored, no one would turn down a random guy walking up and jacking himself off in your mouth, followed by you swallowing. No words need pass between the two of you, just as you would nod your head if any stranger made eye-contact with you on the street. It could simply be like holding a door open for a random stranger in public, followed by a simple 'thanks' in return... only in this case it would be because you just swallowed his semen.
I'm sure some company or corporation could turn cum swallowing into a muli-billion dollar industry overnight.