Ethics and honor are great things but keep in mind we're not a collections agency that's buying bad debt off companies for pennies on the dollar to chase, which sounds like the experience you're referring to.
Or at the very least, stop protesting when people call it out.
So this is already a pretty seedy area of business.
Now add to that the fact that the customer has ignored the payment-failed e-mail, and ignored the warning banners on the site during the grace period, and doesn't mind when they get cut off entirely. Clearly, this subscription isn't producing much value for the customer.
And then consider the ethics of offering expensive services to people who can't afford them. If a person lives in such abject poverty that their bank account has literally zero dollars in it, should I be pushing them to keep their subscription? Even when the service has so little value to them?
It's not technically illegal though.