Would you lay bets against your team to earn some dosh? A Mackem I know has stuck £500 on you to go down at 8/11 a bit back with the logic that the cash will get him hammered- and if he wins nowt you are up.
I had £20 on West Ham @ 5/2. Like you say, it's just logic. Doesn't make me any less of a supporter. If I lose my money Sunderland have done well so I'm happy.
Two arguments, equally compelling. I've won money betting against my team (Liverpool) and did so, as the OP stated, to (hopefully) reduce the (psychological) damage of a loss. I won but felt like I'd tarnished part of my soul! ... And I don't even believe in a soul! Regardless, it made me feel like a part of me had died, and I've never had the guts (if that's, indeed, the word) to do it again. My advice would be to forget about that sort of thing. However, if you can stomach it, fair play. If you have no issue doing it, I'd imagine it'd be a sensible, logical plan. Win-win, in a way. I just couldn't do it after the last time. Each to their own and no judgement implied. I'd do it if I could, for sure!
I've backed against us in the past and will do again. You can't let sentiment get in the way when you're betting. Bookies love people who do.
One of my biggest single wins was against us, 2-1 up at Old Trafford on 90 mins, £50 at 8/1 United next goal. I was gutted to win, but £400 beer tokens softened the blow.