On the whole "animal spirits" thing, furry and therianthropy are not "sister fandoms" as that guy co-hosting 2Sense put it. That being said, the extent to which therians and furries get wrapped up in their respective pursuits is like two sides of the same coin. For example, I know a guy who legally changed his name to "Wolf", which to me seems unnecessary since names are just labels and if you're a wolf, you're a wolf regardless of name. Now, he might be a bit eccentric, but he's not deluded to same extent as people who believe they can or should become more animal-like physically. On the furry side of the coin, you get body modification, and on the therian side you not only get that but "p-shifters" who believe the ability to physically transform one's self into an animal on the genetic level is or will be possible. But then again, you can have delusions and still lead a healthy lifestyle, just as you can change your name and appearance and still lead a healthy lifestyle (the fact that society will make this nearly impossible for people who look too different doesn't necessarily mean they can't be productive members of society. People just won't allow them to).
What I think it comes down to is how much someones obsessions interfere with the rest of their life. Like somebody might not fursuit, body-mod or believe in p-shifting, but instead spend so much time on Furcadia or searching the net for furry art that they neglect school / work and family and their other obligations. And really, that kind of person is more self destructive than someone who wishes they were their fursona / were-side but doesn't obsess over it to the point that it takes a toll on their quality of life.