The difference is that there is wide public support for abortion being legal. While the core of his party might not like it, the average Canadian is OK with abortion being available. So, taking an activist position on an issue like that is problematic for any party that is trying to keep a majority.If Harper is not going to use the CPC majority to do something about abortion (a much hotter 'hot button' issue for religious fundamentalists), there is no reason for him to do it for prostitution.
The situation is very different for prostitution however. Support for that issue is much narrower. At best you could say that the average Canadian doesn't care about the issue. There is no threat to his majority if he legislates against this issue as a result. Because it is not something people feel strongly about there is risk in making an issue of something people don't care (which makes them seem petty and have an agenda), so they were content to leave the status quo in place. Politically he can't be proactive, but he most certainly can be reactive. Now they will present this as a situation where they have been forced to do something by the SCoC. This allows them to follow an activist legislative route with little political risk, in fact it will probably be a political advantage.
The Liberals and NDP are not going to see any political capital to be gained in being portrayed as being on the side of prostitutes and johns, so I doubt they will oppose the government when it comes to the intent of the legislation. Their opposition would just be about things like the penalties and the wording. In fact, they are probably happy that this court decision came down on the Conservatives watch, since otherwise THEY would be the ones having to make it illegal. All three parties would probably have come up with fairly similar solutions to the problem created by the SCoC.






