You cannot consistently say that man has a free will but cannot lose his salvation.
On the other hand, those who believe they can lose salvation by some action of their own, are essentially saying that they must maintain their own just standing before God...that Jesus is not sufficient to save. Not far from Roman Catholicism. Trusting in themselves (partly) to get in and trusting in themselves (partly) to stay in. Thus they believe in the NECESSITY of Jesus grace but not the SUFFICIENCY of His grace.