As many have pointed out, it's not acceptable to just continue running with a broken business model. That benefits no one. But changing your model and either not making absolutely sure to tell your customers or neglecting the attempt is just plain dishonest.
A while back there was a lawsuit over one of the Canadian cable companies doing an opt out (negative option billing) and in general its not really considered a good business practice.
They should make good their customers entire financial loss.
It appears as though they haven't even rectified that. It's still opt out. They're going to email 71 customers asking if they want a refund. What if they don't respond? No refund, right? What about the people who got the first email but didn't cancel, they still get charged, right?
I would find it difficult to trust any company with my credit card info if I knew the only thing standing between me and new charges for things I don't want was reading every email they send me.
they did not convert people to paid members, they renewed existing memberships for people who had not been been notified of changes to policies of the membership.