People already pay for Meetup.com. As an organiser I think I'm paying around $180 a year and that limits me to three meet-up groups under my ownership.
From what I've seen, no one is complaining about paying for Meetup's services. It's the unfairness of the charge that is the problem.
Why is it unfair? For one, meetup attrition is often in excess of 50%. So, 100 people RSVP, you pay $200 for that one event (more than the previous annual fee), and maybe 50 people show up. It's also out of scale with what similar services charge. Another problem is that it makes running a free/community meet-up unpredictable financially. I'm happy to stump up $180 a year if it means Meetup.com makes it easier to grow the audience for a group I run as a hobby. I'm not happy for that to become, potentially, 12 times that.
People are demonstrably willing to pay for Meetup.com. They're not willing to open themselves to unpredictable and, frankly, wildly higher fees just because Meetup's parent company is going through a hard time.