It's not the opinions that are being deleted. I'm sure those opinions also contain personal attacks, off topic remarks, bitches about deletions, etc, etc, etc which get the posts deleted.
Otherwise, they'd be restored upon review by an admin.
Anything we can do about this?
Read the TOU for posting.
You can lead a horse to water. But you can't make him get down on one knee and do an Al Jolson impression!