I have always been a bit ambivalent on this issue. I used to strongly believe that this was a gateway drug and of course, could cause health problems with extended use. Perhaps I am now jaded, but I look at this as drug that, well, no matter what the drug, there will be parts of the population that will become addicted. There will always be some that will consume it to the point of detrimental health issues. There will always be some, with great potential, who will check out of the community (so to speak) to consume this or other drug for the effects (whatever the psychotropic effect it will be).
Will this put others at risk — ie DUI accidents? It could and probably will, it is a depressant like alcohol, and the effect on motor skills, decision making, and reactions will be degraded. However, with legalization of marijuana, resources could be reallocated, tax revenues would be increased, and law enforcement would target the results of consumption (like DUI). I know, as should any legislature, that legalizing marijuana will not result in a world of milk and honey with unicorns painting rainbows, it will still have that intensely personal loss, when someone’s loved one is killed because of chronic long term use or DUI homicide.
It will definitely lead some astray from their potential that are now inhibited from partaking of tokes because it is currently illegal. There will be others, who won’t start because the only real attraction to them is the thrill of illegal. In short, humanity will be just as stupid and self destructive as they are now.