> Other than cost, I see no downside to avoiding seed oils and a lot of upside
The taste of food in certain recipes (that don't involve cooking the oil) varies widely with the oil used. In some recipes, canola oil tastes better than olive oil (by a significant margin - no one would eat it with olive oil).
Cost was never a factor for me (even as a student). Oil is amongst the least expensive things in the food I cook.