The Large One
Who's Next?
Whatever the policy calculations the LibDems couldn't possibly risk being perceived as "propping up a worn-out party that had been rejected by the electorate". In the inevitable second election in a few months' time the Tories would finish the job - as Labour did in 1974 - and the LibDems would be back in phone box formation. But if Clegg supported the Tories on an issue-by-issue basis, with Vince sweeping in and out of Number 11 every other day, they would be seen as Moderating Agents of Change when Election Number 2 came round. It's a no-brainer for Clegg whatever his hairy-toed activists might think.
You could make exactly the same argument with the boot on the other foot as well. If Labour end up with most seats, it would not be unreasonable to make the claim that the electorate had rejected the Tories.
Works both ways.