To your example if McDonalds added cocaine to their fries, we would likely agree that that’s wrong and we should stop that behavior, right?
If it’s more along the lines of addiction like “people love fast food” but aren’t actually physically addicted to it, then I think it’s fine that the business owners make it more delicious or “more addictive”. In that case I’d agree it’s likely on the consumer to make the call. (I’m going to gloss over the realities of the fast food industry preying on lower economic communities and pretend we’re operating in a vacuum where someone has equal agency/ability to go eat McD’s or eat a healthier alternative.)