The reality is that this United side look like they could lose to anyone, so of course I'd love them to beat Liverpool. I'd get my fun laughing at United a week or two later when they lose to someone shit. Nothing about this side makes me think I won't get plenty of chances to revel in their misery, there's no reason to inconvenience ourselves.
I would however be very tempted to trade letting Chelsea (or pretty much anyone except Liverpool) win the title if it meant United getting relegated, as that would be a once in a lifetime event, I potentially would literally die laughing. I love winning the league and obviously want us to, but at the same time know it won't happen every year (and weirdly I don't think I'd actually want us to win it every year like Bayern, that looks a bit shit). If we won the league 9 times out of 10, but in that 10th year United or Liverpool were relegated, I think that would be just about the perfect decade of football for me.