What Layton enjoys right now is leverage. The makeup of parliament allows Layton to be aggressive in his demands. Public sentiment has Harper on the defensive when it comes to the environment, which applies enough pressure to move him more than he otherwise would want. In other words, the current climate might just allow Layton to get what he wants. Assume that Layton does force an ambitious agenda, it just might be worth propping up the government. Afterall, the issue isn't partisan consideration, it really should be about achieving something effective.
If we do go the polls, with no progress on the Clean Air Act, there is no guarantee that the future looks brighter. Layton forces an election, with the knowledge that the next parliament could well see another Tory government. If Harper were to win re-election, the leverage is gone and Harper would be more inclined to produce his own legislation, independent of others. You have to wonder if an emboldened Harper would mean a less effective piece of legislation. In the aftermath of an election, the government has the momentum, as no one would accept another quick vote.
The problem for Layton, despite what could be achieved on the environment, there will still remain a myriad of issues that contradict any "alliance". It just seems counter-intuitive to believe the NDP rank and file would be comfortable with Layton propping up the government, for any length of time, no matter the one "result". If Harper did agree to Layton's demands, you woud assume there is some assurance that Layton wouldn't turn on the government quickly. You have an important achievement, but there still remains the inherent contradiction on so many other issues. Layton is in a tough spot no matter where he turns, both ethically and politically.
Interesting Travers piece that suggests another consideration:
If Conservatives are successful in sweeping the environment off the table, voter attention will shift from monumental issues to the more mundane management of national affairs. Advantage Harper and the ruling party.
If Layton helps Harper take the environment off the table, does he in fact remove the achilles heel and all but guarantee a future re-election? You help your ideological foe, ensuring a longer neo-con reign.