Defamation is when someone writes (libel) or speaks (slander) materially false facts about someone else to a 3rd person where those facts damage that person. Opinions don't count, and damages are fairly hard to prove.
But if you don't defend yourself, you'll make things much easier on the plaintiff. You've got 30 days from the day you were served with the complaint to file a response or you'll lose by default. so get a lawyer NOW. You can "flatly refuse to pay" but you may not have a choice in the matter if this plaintiff gets a judgment against you. In CA, judgments are good for 10 years, and are renewable for successive 10 year periods, so even if you're broke now, maybe you won't always be, and plaintiff can levy your bank accounts, garnish your wages, record the judgment in every county you own real estate in, and the judgment will grow by accruing 10% post-judgment interest until you pay it and show up as a big negative on your credit report.
Jail isn't a worry, there's no such thing as debtor's prison. But even if you have other debts for which bankruptcy is a reasonable option, defamation isn't normally dischargeable in bankruptcy, so you really have no choice but to defend this lawsuit.
As the for the merits of plaintiff's case, there's no "provocation" or "self-defense" defense to defamation, but you may have other defenses, such your statements being not recognizably about the plaintiff, or that they were not actionable opinions. if you qualify, maybe you can get a free lawyer from Legal Aid.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Before you completely give up I suggest you contact an attorney. Some insurance policies will cover defense of libel/slander cases.
IMPORTANT NOTE: These materials have been prepared by Adina T. Stern, A Professional Law Corporation for informational purposes only and are not intended as legal advice. The information available in this answer is not intended to create, and receipt of it does not constitute, an attorney-client relationship. The information on legal issues available here is not a substitute for legal advice from an attorney who is familiar with all of the facts surrounding your particular situation who is licensed in the appropriate jurisdiction. This answer does not create an attorney-client relationship.
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