The problem I see is that many so-called Christians are not born again to start with. Paul Washer is somewhat extreme, but he has a point. Surveys reveal that the great majority of church attenders are Christian in name only. This clouds the issue. If pastors would preach the real gospel and ensure that their congregation consisted of born again believers, we would be having much different conversations. It varies, but something like 3-4% of church attenders are in reality born again.
I agree absolutely that once a person is born again, he cannot be "unborn" again. Eternal life is just that - eternal. What confuses people is that there are two salvations, or three really. The first is to be born again, as you say it is instant. Then there is the salvation of the soul. Some call this progressive sanctification. I don't know why. The Bible states "the salvation of the soul". The third is that our physical bodies will be replaced. That also will be instantaneous.
If we replace "salvation" with "deliverance" it makes things a little clearer. Lord Jesus preached and ministered deliverance. Our ministry should be His, as stated Luke 4:18. The born again should be changing over the years. I knew nothing of any of this when I was born again. 50 years down the track, I am a different person. It's not my doing. All I've done is sin and fail and stumble and fall. "By grace are you saved" is a moment by moment experience, not a one off the time that you are born again.
To hell with "isms". They just divide and detract from the true gospel. Jesus came to give us new life, not a new theology to argue about. Can we not just focus on Lord Jesus, who He is, what He has done for us, who He is in us and who we are in Him? We argue about non-issues while the world drifts along the road to destruction. We don't have time for this.
While there certainly are false converts out there, Gideon300. Nevertheless, the problem with Paul Washer and John Macarthur and other Calvinists and Lordship Salvation proponents is that they equate continual carnal living as "evidence" that one is not "really saved." And this is not the case at all. Since any Christian is capable of committing any sin of the flesh. A Christian that lives in carnality is simply a Carnal Christian. And one that is still immature.