Paying for a service you use is fine, nobody owes us anything for free.
That said, $50 a year is just too much for what I am using Flickr for - mainly, browsing through personal photos so that we could watch them on our phones and tablets from anywhere.
I just realized that Amazon Prime Photos provides unlimited full resolution storage and backup. Since we are paying for Prime anyway, and getting very good value out of it, I will most likely move all my photos to AP and only keep my Flickr account for sharing to groups. APP is fairly limited as far as photo management (e.g. no way to read Exif) but it's good enough for what I need.
Given how cheap it is to store terabytes of data, I think SmugMug could easily lower the price for basic accounts to $20, offer say 250gb vs 1 TB, make videos a Pro feature, and still make money on people who are otherwise going to leave. Their bet is likely that enough users will convert to the $50 account to justify the hike.