Why are seed oils unhealthy, though? I can't find anything that's bad about them in particular. I've only seen people commenting online saying to avoid them.
There's too much there for me to give a great answer here, but I can recommend Dr Michael Eades as a starting point. He wrote a couple books over the years on heart health and has been writing a newsletter for the last few years where he discusses various related topics in detail.
At a super high level, it has to do with how seed oils ("vegetable" oils, etc) are produced and how oxidative they are in the body.
