Perhaps I should ask the question in a different way, do you believe that the number of silencers possessed by criminals will remain the same regardless of whether they become legal here or not?
No. I think it's all a matter of availability. Right now, there is no availability, so the use of silencers in the commission of a crime is unheard-of. When availability rises to "some," the use of silencers in crimes will be "rare." When availability rises to "commonplace," the crime statistic will rise to "not uncommon." And by the time legal silencers are as commonplace as rubber slippahs, the crime statistic will approach "nearly half."
Whatever mechanisms exist for putting firearms in the hands of criminals, these same mechanisms will presumably function for other items, including silencers.
Note that FBI statistics do tell us that handguns are far and away the weapon of choice to use in
murders. This implies a degree of selectivity and practicality in the criminal element. Those same characteristics are going to suggest that a silenced handgun could be a "better" choice.
Again, though, I don't feel this is the argument we should be making. It doesn't matter if we're talking about handguns or oranges, someone is going to find a way to abuse them. We should instead focus on things like cost/benefit analysis and overall statistics of abuse rates.