Legal Question in Civil Litigation in California

They didn't demur, they answered. Every answer says the complaint fails to state a claim upon which relief can be granted. It is standard boilerplate.

Mr. Stone is correct that it is a standard "boilerplate" affirmative defense, but let me elaborate for you a bit. Suppose you plead that your friend agreed to loan you a dollar in return for $1.10 in a week, if he had one in his wallet. In reliance on that, you ordered a hot dog from the cart nearby. Your friend didn't lend you the dollar. As a result you didn't get the hot dog that you had agreed to deliver to your neighbor for $1.50. So you sue for your lost profit of $0.50. You have failed to state a claim on which relief can be granted, because you alleged a condition on the loan agreement: that the friend have a dollar in his wallet, but you failed to allege that the condition was satisfied: that there was a dollar in his wallet. If your friend fails to raise that defect in response to the complaint, he waives it forever and you will later be allowed to introduce evidence that he had the dollar in his wallet. He can file a demurrer now, but it will be granted with leave to amend. Or he can plead it as an affirmative defense. That preserves the issue for a motion for judgment on the pleadings later in the case. Since lawyers usually have a fairly tight timeframe to respond to the complaint, and since demurrers can be relatively costly, requiring drafting of a motion, a legal brief to the court, a reply brief to any opposition brief, and a court appearance, and since leave to amend is liberally granted, it is the usuall practice just to plead it as an affirmative defense and then see later if there's any defect in the pleading that could not be fixed by amendment.

Lastly, to answer your question directly, if you think there is a defect in your pleading, it is better to amend now than let a bunch of discovery get done based on the pleadings as they stand, and let the case generally get closer and closer to trial before amending. Leave to amend is liberally granted early in the case, but as a case goes on, eventually you would prejudice the defendant by amending too late and leave may be denied. However, once the answer is filed, you must have a stipulation or a court order to file an amended complaint. So if you think your complaint is sufficient to state your cause(s) of action, leave it as it is.