Yes, it makes sense ethically to push the FDA not to approve a drug you think won't work. It also makes sense financially to bet that the FDA won't approve a drug that you think won't work. But it doesn't make sense ethically to do both, both directly because it creates a conflict of interest, and indirectly because that very conflict of interest undermines both the objectivity and the credibility of your recommendation not to approve the drug.
You are arguing ... what, here? That people with some sort of knowledge of a product/company/industry's prospects shouldn't be allowed to buy/sell positions in that company?
If I understand you (and I may not), and we were to come to the conclusion that "there ought to be a law", I have no idea how that would even be structured/written.