You don't even need to be firm or argue. I've had to cancel my NYT subscription several times over the years. Sometimes I moved to a place where delivery wasn't available. Others because I was between jobs. The people on the phone are very polite and professional. They will offer you discounts, but they won't ever give you a hard sell. At least in my experience.
Do they offer intractably complex subscriptions meant to deceive you into buy more than what you need ? No.
Do they prey on old people and talk them into services they neither use nor understand? No.
Do they call you on a regular basis to nag you about an upgrade to your subscription? No.
Do they send you mail 1-2 times a month with one of those stupid credit-card-sized cardboard ads with a deal on them? No.
Do they automatically jack-up your bill as soon as intro is over? Yes. That's about as close as they get to cable TV. It's not good, but it's not evil either. You can, AFAIK, extend a discount indefinitely by calling them up and asking for it.
They create an "obstacle" to cancelling your subscription. The "obstacle" is you have to make phone call and talk to one of their agents who will try to keep you as a subscriber by offering a discount on the subscription.
It's a good way to extend your introductory payment plan (or close to it).
You can still cancel, of course, just be firm and say so. Not a big deal.