Avoiding offense when asking about taking a course without watching lectures
I doubt many people would take offence at only the suggestion. More so if you have a reasonable reason, such as sitting somewhere else in the campus.

And if the professor gets offended by that, you wouldn't be able to take the course anyway, so the damage control is in place (and honestly, you have learned of a professor you probably don't want anything to do with).

On a side note: the value of lectures vs slides and books alone depends more on the lecturer and available books than on the material itself. For example, if you look at any of my slides (regardless of the topic) without me talking, is going to be cryptic and uninformative, because I don't design them to stand on their own. On the other hand, if you have listened to my talk, they can be a good memory refresher of what I said.