If it is a movie I want to watch, I don't mind buying it. I am then paying for the convenience, the option, to watch it again at any time, rather than waiting for a Netflix delivery in x days/weeks, or going to a B&M store/kiosk, then returning to the B&M store/kiosk at a later date.
Sure, there are movies I watch once and then rarely/never again, but the convenience of being able to watch the movies I truly enjoy is worth much more than the $8-12 I'd have saved by just renting it.
If it's a movie I am not sure I want to watch, then I get it on sale or I never watch it, unless I happen to catch it on TV at some point.
I am a buyer, a collector, renting just seems like a waste of money.