I am not religious, but I feel that one of the services that the church has always provided was to be a place for the down and out and needy to find some solace. Charging to use churches would only hurt the people who probably feel like they need it the most.
Generally speaking, religion is a construct for moral positivism. Charity is a manifestation of this moral positivism. Members of a congregation should willingly opt for donation to their church. If a member does not opt to donate to their church, the message has been flawed in some way and the church may need to rethink and change the approach to their sermon.