The current pop-sci theory is that arachadonic acid (an omega-6 fatty acid common in seed oils and which your body produces from linoleic acid, another omega-6 fatty acid in very very high concentrations in seed oil) is pro-inflammatory. In my view, while this is not strictly wrong, it is misunderstood and people draw incorrect conclusions from this.

The takeaway I would suggest is that you cannot possibly know and acount for all of the psychological processes involved in anything. Looking at one physiological process means nothing in a complex system like a human. Drawing some conclusion that "seed oils are inflammatory so you should avoid them" based on this fact in isolation is just folly. To know the truth you have to expose a lot of these complex systems to a lot of seed oils.... and that has been done. And nearly all of these studies show high seed-oil intake leading to longer lives, less heart dieases, less diabetes, and numerous other positive health outcomes.

And no, I don't work for big-canola.