The problem with this change is not that Reddit has costs that they are trying to recoup. The problem for me is that much of the user-generated quality content that Reddit is trying to monetize was created, by users, under certain assumptions. Then those assumptions were changed for a short-term monetization gain.

If they initially said that they will be requiring sing-in to read comments, push app over browser, etc. it would be just fine (but then I suspect they would not have any quality content to monetize). Just my 2c.