working out at a fixed % of AT will make sure you cross over into anaerobic everytime. That is true. but at the same time, you will have to do more and more work to get to that point, and I think people underestimate how much that is (and thus get frustrated with cardio and blame exercise in general, poor genetics etc.). Purely as a time measurement, the amount invested just doesn't make sense vs. lifting. why not just cut to the chase and start with anaerobic exercise, since it looks like we agree that that's what burns the fat?

edit: I should also reiterate, as many have below, you ALSO get the cardio benefit from lifting.

"working out at a fixed % of AT will make sure you cross over into anaerobic everytime. That is true."

No, that's completely false. It doesn't even make sense.

If that fixed % breaks your AT it does. Which is what happens if you lift heavy weights with a decent speed right?

If not please explain, I'm a bit new to the concept.

Let's say your anaerobic threshold is 190bpm, and you are working out at 155bpm. That means you can never go over your AT by definition, since you are always changing your pace to keep your HR fixed at 155. Essentially the longer you work out the slower you go, so that your heart rate never increases.