Whenever I get into a discussion about whether or not a person can lose their salvation and the person tries to make it a Catholic vs. Protestant issue I hope I can remember to tell them, "Take it up with the Methodists." Here is a discussion from an official Methodist web site answering the question...

Do United Methodists believe "once saved, always saved" or can we "lose our salvation"?

The bottom line will then be, "On what basis are the Methodists wrong, and you right?"