I would think sucking out even some of the poison would help. And if you used a plastic bag or ??? as a barrier, then none of the poison would get into contact with your mouth lining…So why not suck on a bite until you get to a hospital?
-Tcat
Actually, sucking out the poison could help the victim, just not the good samaritan. Most carry-around type snake kits actually have a ‘sucker’ that pulls out the venom, kind of like the human mouth would. So it is not really a myth that sucking out poison does not work. But what happens to the sucker? Where does the venom go? And the sucked (love these scientific terms I am using) could get an infection from the saliva of the sucker.
Of course you come up with the plastic bag. Well, if you have a plastic bag with you when someone gets bit, why not just have a snakebite kit? Also, it would be a little hard to get some sucking force with that bag there unless you cut a hole in it, and that kind of defeats the purpose.
I say just kill all of the snakes in the world. Yes, we might get filled with rodents, but no more worrying about sucking out snake venom!
Actually, I believe one of the reasons that sucking snake bites is discouraged is that it makes identification of the venom significantly harder, as much less venom is available at the site of the wound.
Lance, ummm, think about your physics again. There is no hole needed. Otherwise, other barriers with holes and other forms of sucking wouldn’t be quite as safe, eh? 
Plus, people have many more plastic bags in their picnic backets than snakebite kits when they go out into the mountains/fields.
-Tcat
IIRC snake venon can go through the digestive system without harming the individual if the individual has no lacerations/ulcers in the digestive tract (basically the venom does’nt come in contact with blood).
So the good samaritan is exposed to some danger IMHO.
I think this is probably one of the main reasons not to suck on snakebites. You don’t want someone else’s mouth coming into contact with a break on your skin. There are all kinds of nasty things that could pass into your bloodstream that way.
I believe the reason for no longer recomending sucking on a snake bite is that it was found to be ineffective. A quick google turned up this site , and here is more information on the Sawyer extractor.
From what I gather the Sawyer extractor could outsuck even Linda Lovelace. 
AFAIK some kinds of venom can be absorbed into the bloodstream through the gums.
Twenty-plus years ago, most first aid kits for the outdoors included a knife and a suction device, to be used for “cut and suction” first aid of a poisonous snakebite. What follows is what I was taught in Red Cross first aid training at that time. Considering that more hospitals have been built and cell phones weren’t in existence back then, the advice should be even more applicable today.
The complications arising from cut and suction are usually worse than the relief given. Given that a snakebite is a puncture wound, you have to widen and deepen the wound to get to the venom, then the person giving first aid has to either put their mouth or a suction device onto the wound and try to draw the venom out. Either way, you are also putting spit or who knows what into a moderately deep wound and contributing to the risk of infection.
On the other hand, most hospitals either have antivenom or have ready acces to it, and people are very rarely more than a few hours from a hospital and can call for assistance or if there is any doubt.
Also, rattlesnakes (to name one species) release venom in only one out of seven strikes. The rest are simple (though painful) puncture wounds which suction would only aggrivate.
Also, in the continental U. S., at least, even envenomed snakebites aren’t very serious. As I understand it, over 95% of rattlesnake victims will survive even without any treatment whatsoever. If you can get the person to a hospital, then survival is almost guaranteed, with no need for any sort of first aid in the field.
Boy, that needed a rewrite…
(Quoting myself as a reference? I’ll try to work the royal “We” into my next post.)
I guess my main concern is not only survival, but of lessening the effects. Even though most people survive, have you seen the damage done ?!? Dead skin, lost fingers, swelling up like a balloon…If sucking out a tiny bit helps relieve some symptoms, then why not?
-Tcat
Because it really doesn’t help, and introduces several additional risks.