Their decision to block port forwarding was unfortunate, but understandable. I've been using it for the past year and when I first started, I rarely ran into any issues with being blacklisted. Now it's a nearly daily occurrence. I don't know how true it is, but Mullvad claimed that much of the activity leading to blocked IPs came from activity related to port forwarding. If that's true, then I'd say the decision is good. Like others have said, torrenting is still possible without port forwarding, but it's also true that rarer content and private trackers become difficult. Ultimately there was no perfect solution here.