On the airplanes I don’t have a problem with there being a service charge.
In the airport (which can be publicly built) may be a different breed of animal.
Additionally, I didn’t like the United gave 1 hour free (not cumulative but clocked from initial login) with $8 or so for a day’s use. Well typically you will only wait at a gate for an hour. I got stuck waiting 8+ hours in good clear weather and kept getting 1 hour and 2 hour delay notices. If they’d been upfront about the TRUE delay I would’ve opted for the service. So I never got to use my computer in the remaining 7 hours (nor did I use more than 15 minutes total). Making the gates free is at least a small comfort for the passengers on delayed flights.
Even if terminals are publicly built, why should valuable products or services be given away? No one would expect free food service in terminals—why should internet be any different?