Leftist First, Catholic Second

For too many Catholics and other Christians, their leftism is their real 'religion.'  This from The Thinking Housewife:

ANNY YENNY reports at the website Politichicks that her eighth-grade son was given extra credit by his Catholic school religion teacher for fasting on the first day of Ramadan. When the mother complained, the teacher objected and “lectured [her] on the superiority of Muslims to Christians.”

The principles of ecumenism put forth at Vatican II lead with irrevocable logic to teaching Catholics how to be good Muslims.

I agree with something in the vicinity of the point the Housewife makes here.  But her last sentence illustrates the slippery slope fallacy.  If the logic is "irrevocable," then it is deductively valid; but slippery slope argumentation, if intended to be deductive, is always invalid.  What should she have said?  Something like this: 'The ecumenism of Vatican II set the stage for, and made likely, the sort of absurdities that Anny Yenny complains of." 

Surely there was no logical necessity that the principles of Vatican II eventuate in the absurdity in question.