All i can say is that there is already a legal substance that does all the same things you stated in your second paragraph... ALCOHOL. Alcohol ruins peoples lives, people who are not responsible with it, and for that matter i say why should alcohol be legal and cannabis not? The fact that yeah it makes some people complete slobs who don't take care of them selves is true, but when you say "some people" that leaves it up to personal interpretation, no cold hard facts. I would also like to know how you think that cannabis would take away a mans strive to "get laid" as you put it... I didn't know that was even possible. I agree that yes there are some smokers out there that flaunt their use of cannabis to the point of douchebagery, but seriously how many people do you see like this? And if they're not your kind of person, well then don't affiliate your self with them. As for the gateway drug part of things, think about it this way: If you didn't have to get your greens from a dealer, who more than likely deals more than cannabis, would you really ever be subjected to anything else other than cannabis? Take the underground market out and bye bye dealers.
Oh and by the way you contradict yourself when you say that quote "I've never known any of them to be the type of person who tends to go out and have a good time - to party, meet people, get laid." then later you go on to say "I think that people should feel free to try pot. People should feel free to use it responsibly in a social situation." Partying/having a good time are social activities, in which you say people should try it then, but if people who smoke don't do those things (meaning they wouldn't even be at the party/having a good time) then how would people try them in the first place?
Everything in moderation man, once it becomes your life its gone to far. You have much to learn my friend, it seems like your times in the good life were either short lived or you just can't live them anymore so since you aren't one why not hate on it.

I agree that yes cannabis is addictive... although it is one of the easiest substances to "kick the habit" in the world. yeah your gonna feel like shit that your not on flying high cloud nine anymore, but its only mental, unlike alcohol, painkillers, or tobacco for that matter, in which they give you psychical withdrawals. from personal experience after being addicted to hydrocodone for a year vs quitting bud after a year was astronomically easier. also agree that these are some broad claims due to the fact that cannabis research is stunted due to its illegality, but there is some scientific proof to most of them.