I think the implication is that a product can do some harm, while reducing the overall harm in the system. In this case, vaping might cause some harm, but it potentially reduces the overall harm by doing much less harm than cigarettes. I believe the comment is saying that, by pushing for regulatory approval, the product may never enter the market and would thus not be able to reduce the overall harm being done.

In this case, we would certainly have to consider the potentially increased harm of non-smokers taking up vaping to assess the overall harm being done, but I see the merits of the basic argument at least.