The point is not just about Sprout (we all know it had critical flaws). It is about trust. Even the transparency promoters is Zcash claim users have a choice to use transparency or not. That will turn into a lie if Sprout funds are seized for all users not willing to use transparency in the turnstile process.
If the above scenario occurs why would any privacy purest (that never wants to use the transparent pool) ever trust Zcash again? What guarantees are there that the same thing wont happen to Sapling or Orchard pools when/if they are depreciated one day?