Marijuana use has yet to be correlated to accidental deaths in ways that hard drugs such as cocaine, heroin, or methyl-amphetamines have. Furthermore, alcohol-related deaths, accidents, property damage, and rape significantly outweigh the problems that arise from even excessive marijuana use.
By legalizing marijuana safety measures will be put in place which will markedly lower the potential negative effects of marijuana use- namely cancers. Can anyone tell me if they use a filter on their bong or blunts? Because I certainly never have. State-regulated marijuana use will almost definitely require that marijuanarettes (i should trademark that

) have filters.
Also, state-regulated marijuana will have to meet certain criteria for potency. Imagine never having to worry if you dime sack was garbage, or being able to go to the store and purchase varying strength marijuana. That would be amazing, in my opinion.
For all the haters- I'm fairly certain that Obama isn't trying to pass legislation DEMANDING the use of marijuana. You will still be free to abstain in the way that you do for cigarettes. Marijuana drug enforcement wastes untold amounts of tax-money that could be more responsibly allocated to preventing adolescents from getting involved in the traditionally 'hard drugs'.
Furthermore, teens and college students who are nabbed for their generally innocent use of marijuana have had their lives drastically changed. I have in the past had friends kicked out of college for repeat offenses against the marijuana policy. I know people who now have permanent records for possession of weed and have to write down on their job applications that they have a record because of 'drug charges' These students who were doing nothing to bother anyone else, were denied their chance to complete college for something as simple as smoking a few spliffs here and there. Personally, when I was in college, I found the raucous caused by drunken idiots to be FAR more distracting to me than the occasional pleasant whiff of weed.
Quit hating and move on. It's just weed. (and please, for everyone's sake, don't turn my, 'it's just weed' comment into a slippery slope argument, because that's just retarded.)