Lying is bad. Lying to stop people from doing something is stupid, dishonest, ineffective, and bad.
Health education in the US has determined that if you do drugs you are Bad, and pot is a drug, so if you do pot you are Bad, so that everything possible must be done to stop you from using pot. This extends to distortion of facts, exaggeration, and flat out lying.
Pot is not a gateway drug. Such things don’t even exist. The only reason you’re more likely to do other stuff if you do pot is because if you’re more likely to try pot, you’re more likely to try other stuff. Logic 101.
Pot is not uber-super-hyper-mega addictive. In fact, cigarettes are as or more addicting.
Is it bad for you? Abso-f’rigging-lutely. It really can do a lot of damage to your lungs, and it really does have a lasting impact (with extended and moderate or high use) on the brain.
But lying about it just gets people to ignore you. If you’re lying about half of it, it’s understandable and reasonable to assume that you’re also full of it about the rest. This is one of many reasons that, to be honest, US health education often does as much, or perhaps even more, harm than good