That's not how it works :)
Your defense says you deny owing the creditor and requires the creditor to prove their claim. Common points listed on a defense are:
1. You deny that the creditor is owed as stated in the claim.
2. In the event that you are indebted towards the plaintiff (which you're not admitting to) you believe the amount requested is in excess of the actual amount owed and require proof of the amount claimed.
3. You request the court costs to the plaintiff not be added towards any judgment that could be awarded.
Obviously, I'm not a lawyer and they would word a defense correctly and assist you with every possible defense point that can be added, but these are the common ones I've seen.
The reasons for the above points are:
1. The creditor may have lost the agreement or application. If those aren't available to them, you could have it thrown out or at the very least make it far more difficult for them to obtain a judgment searching for some other type of signed document then having to get the court to agree that it is as valid as the signed agreement would have been.
2. The amount ALWAYS should be questioned. Johnny lawyer can put any amount in the claim, make him prove this with an actual printout of the account history. Many claims are adjusted (lowered) when it turns out the lawyer 'accidentally' listed a higher amount on the claim than what was owed.
There are multiple reasons an incorrect amount can be listed, but it's common enough that you should always question where the amounts coming from that's being listed.
3. You could have a lesser amount of the costs added or get a break in some way. Not likely, but it does happen and there is no reason not to request this especially if payments were being made to the creditor and they sued anyway.
Lots and lots of options when you file a defense, whereas if you just let a creditor get a judgment, you're stuck with that.
The hassle to go and get that changed is far greater than ensuring the action is originally handled correctly. Why should the courts amend a judgment that a defendant was to lazy to defend in the first place?