Running and operating a community and server is hard and it costs money, some people want to do it from their own pocket (as we did with this forum for a long time) and others want to recoup costs from their users. This choice is entirely down to the server and community operator, it is not the choice of users.
If you as a user are unhappy with a server charging for access then you don't need to play, if you absolutely must voice your opinion you can do it via a private message. Anyone found to be posting in SMP threads about how it's a "scam" to charge for access to a server will be warned, there are no exceptions.
It is not illegal to sell access to a server, it is not a scam to sell access, it is certainly not against the rules.