If you get a possession charge, it can be on your record for a number of years. That means potential employers are likely to see it. I'd rather not give them any reason not to hire me, therefore, I avoid marijuana. If you want to smoke it, that's fine. However, to say it is harmless isn't true. It can cause things that may affect others more than the user, such as impaired perception or loss of coordination
when used irresponsibly
. The biggest example I can think of would be operating a vehicle under the influence. That sounds pretty harmful to me. It comes down to being able to responsibly use anything. Alcohol, weed, cough syrup, whatever. If you know your limits and control yourself, it can be safe, but at the same time it can be incredibly harmful if you're negligent.