Cannabis causes less harm than cigarettes?

it's worth keeping in mind the herbicides & pesticides used to grow marijuana. Although marijuana is normally considered chemical-free, technically most is not for that reason!

Long term yes, short term no. Cannabis is a naturally occurring substance on earth, whereas cigarettes are a combination of many "foreign" things to our bodies which will cause long term damage. That's not to say that either one are "healthy."

I'm pretty sure that cigarettes are more likely to give you cancer because of all of the "artificial" chemicals in them. Cannabis (Marijuana) is of natural material. So I would believe so.

While walking across the street, getting hit by an SUV, is better than getting hit by a truck?

Yes, but that doesn't mean you should smoke it though.