If the game has actually been lost (80 popcap for the enemy) - you can't cap anyway.
If you still have units and the enemy can't be bothered to fight off back-cappers, no matter how much they're winning in terms of leftover units, back-capping is a legit way to get a win ;P.
Like Fuck it is.
If I've smashed your entire army and you only have one squad left, and I have say tanks that can't cap. You don't deserve to win. Anyone is fucking moron if they support that as a legit game plan,