Well, the debate regarding smoking causing cancer is pretty much settled, except for about 3%.
As for billboards being censors, I think they should have discretion about what they put up. If I had a company that put up billboard signs and someone contacted me asking me to put up an ad claiming that vaccines cause autism, I think it would be unethical of me to put that up. I could be KILLING someone by accepting that contract.
Friends of Science was founded out of the Canadian Society of Petroleum Geologists and while their funding is not something the group shares many critics claim they have a lot of funding ties from industry. Proper discourse is disrupted when money is paying for disinformation. I think those who spread information should, ethically if not legally, discern if the message they are portraying is dangerous.