The big difference is in that. In double predestination you are born elect (or born doomed to hell). And there's nothing you can do, say, think, etc. etc. to change that.
As some have demonstrated, you can leave the Church. And a I demonstrate, you can join the Church.
yes, but the Catholics maintain the Catholic church is the vehicle of salvation. By baptising infants you are what? baptizing them into the Catholic church? Because they did not make a conscious choice to follow Christ and be born again. and that my friend, is a world of difference.