Well, regardless of they go paid or free everyone is free to use them or not. A bad product cannot survive whatever marketing gimmick they try.

Also, I agree maintaining a great FREE product with increasing user base is not economically viable. You need money either from one way or other. If their FREE model has not failed, may be instead of getting money from users they would have been seeling something else like something based on their vast user database.

Also, whatever anyone does, their is bound to be some criticism.