Eeeehhhh, I don't think so. Hell, most of the time I just allow Silence to run its course without even purifying it because there's way more scary things out there like area Stuns every 15s... Stun is a Silence, but better. And much more dangerous.

If anything Polymorph should be destroyed in order to just... Become Silence. Y'know, exactly what Polymorph is, without the expection to Purify. You wouldn't even need to write an exception to Guard on Polymorph if you did it.