In fairness to him I think it's something you'd need to find out more about the political context of before you outright condemn him. It could quite plausibly be the case that with Labour and the Tories both backing the bill the LD Whip's office told those MPs who weren't going to be in Westminster anyway not to bother about it. It's not as if ours is a system in which an individual MP can do much to affect the passage of a bill - you can't filibuster for example. While it might have given an opportunity to grandstand which you or I would have taken up, if it's a forgone conclusion that it's going to pass I can understand those who aren't especially passionate about it asking what the point is.
Incidentally, I notice duggeh's website says David Howarth turned up for it. You might try emailing him. I know he isn't your MP but I've only ever got straight answers from him so he might shed light on the above. In the meantime your ire is better directed at the two parties who supported the bill rather than those who opposed it but didn't have the time to spend on a lost cause. Perhaps a hung parliament would mean that legislation might actually be properly debated in the future....
I'm composing a message demanding an explanation.
Yeah, that's probably the way to go.