I think the onus in the question at the top should be reversed.
It's the responsibility of socialists to organize the working class.
For that reason I think the NDP, if it is a socialist party, should focus on issues that unite people as a class.
A campaign to end funding for Catholic schools, no matter how it's explained, will divide people along religious lines and give parties like the Liberals all the excuse they need to avoid talking about issues of class.
So, I think the real question is what's the socialist case for making this the defining fight of our times?
And, more importantly, for the "socialist" caucus, what's the "socialist" case for this issue that's so strong you're backing the most right-wing candidate in the leadership race, one who supports corporate tax cuts and pursuing more corporate donors?
Well, I don't think anyone (not even John Tory) would rank this as their #1 issue, but it doesn't make sense to only talk about the #1 and completely ignore the #2 and lower issues.
Also, the NDP is not a socialist party and the Socialist Caucus (and Fightback, the IMT and any other tiny entryist trot group) is a joke.