The defendent always starts with a presumption of innocence.
In this case, the prosecution will have ample evidence to show possession of a silencer and it will be the defendant's burden to prove that it's not a firearm silencer. We could claim that there's a presumption of innocence, but since we know that the prosecution already has sufficient evidence to convict in the absence of an effective and reliable defense, that presumption is already nullified in this situation.
Plus, you'd have to have it on a firearm to be in violation.
We know that's not true. You don't even have to own a firearm to be charged with illegally owning a silencer. A silencer itself is the regulated item. It doesn't need to be attached to anything for a violation to occur.
You CAN'T remove one from an air gun and install it on a firearm without making adapters.
I agree, that's a step in the right direction, but I think that's a thin strand from which to suspend your continued freedom.
By this logic, a silencer that hasn't been threaded for attachment isn't a silencer. That would mean that anyone could make a fully functional silencer and simply leave out the step of cutting the attachment threads and that would make the device not a silencer.
...it's not hard to prove that an LDC is NOT a silencer.
So far I haven't heard any strategies that would prove effectively and reliably that a detachable airgun silencer is not a firearm silencer.
You could attach a lawn mower muffler to a firearm...
That's already been covered adequately. A thing that is not a silencer is not a silencer until there's some additional evidence that it has been repurposed to be a silencer.
That's not the topic under discussion. In this case, the item in question IS a silencer and we know that it can be proven that it will function as a firearm silencer. That's a very different situation than having a common everyday item that COULD be repurposed into a silencer.
If LDCs were illegal, the ATF would have been all over the makers by now.
Here's a project, requiring only minimal effort. Contact all these makers and ask them if they have proper federal paperwork for making firearm silencers. When they answer in the affirmative, ask them why they would go to the trouble since they're only making airgun silencers.
...the courts put this subject to rest.
That's a simplistic view of a topic which is quite complex in practice.
I'm not telling anyone what they can/can't, or should/shouldn't do, but I do think it's important for everyone to understand that there are pitfalls here that we need to be aware of.