I reject the argument that such activity is a privilege to be taxed.To be more specific, the $200 excise tax is for the privilege to manufacture a silencer or to transfer a silencer.
Congress knew they had no authority to ban manufacture, transfer, or possession of NFA items. That is why they chose to apply a prohibitive tax instead. (Thanks to inflation, the tax is no longer outrageous, but the process is.)
Rights versus privileges is a specious argument. Free people have both rights and privileges, and a constitutionally limited government may not infringe upon either.