Nothing I stated made any sort of judgement about whether or not something should or should not be advertised. The original statement (quoted in my previous response) was that someone opposed to an advertisement was "not allowed" to oppose that promotion.
Quite frankly, nobody should be in charge of regulating the messaging. That sounds like top-down control which does nothing but solidify the positions of people/organizations that are already in power and can afford to lobby for such regulations. It's often known as regulatory capture.
There are clearly groups of people that "oppose harmful things" (which is quite vague, but I digress), and have carved out parts of the market that agree with them (e.g., organic foods) and are quite profitable.
Basically: if you propose a billboard saying "Coca Cola Is Proven[cite] Bad For Your Health" you won't be granted any space.
And even if you find a space not monopolized by such committees, you'll be taken to court by expensive lawyers over defamation or trademark infringment or any other silly thing.
Perhaps you should reassess your messaging.
It seems to have become very en vogue over the past 5-10 years to just simply attack someone/thing that one doesn't like, as opposed to providing useful information and allowing people to make up their own mind, or putting the effort in to develop/provide an alternative.
Ultimately though, if your speech is being restricted, you have a government problem.
You are certainly allowed to. Pony up for the ad space if you want to promote the opposite, or advertise something else entirely.