The Mississippi lawmaker proposing a bill that effectively bans masturbation for men says he's shocked by how upset some dudes are ... 'cause he's getting death threats!

MS Sen. Bradford Blackmon tells TMZ ... men from all over the globe are livid about his masturbation ban idea, and they're leaving him "vile" messages ... with some even threatening his life.

Blackmon tells us the proposed bill is legit, but isn't serious -- his true intention was to start a conversation about the double standard between women and men concerning reproductive health -- but he's taking the death threats seriously ... reporting them to authorities.

The "Contraception Begins at Erection Act" aims to block men from spreading their seed unless they intend to make a baby -- effectively outlawing masturbation -- but Blackmon says he introduced the bill to start a conversation about all the regulations put upon women when it comes to reproductive health.

Blackmon says he figured the legislation would mostly be laughed off at worst ... but some guys clearly don't think the prospect of paying stiff fines for solo ejaculation is a laughing matter.

Women, on the other hand, are having a nicer reaction ... Blackmon says lots of ladies are thanking him for his intention behind the bill, which he says is all about making people stop and think about double standards.

Mississippi currently prohibits abortions for most cases and Blackmon's bill is unlikely to become a law in the deep-red state ... but that's not stopping death threats from coming his way.