The doctrine of Once Saved always Saved very often causes controversy among fellow Christian believers for it is very tender and fiercely debated topic and each side or each sides advocates have very strong scriptural references to support their contention or position. This, at times, fierce contention among Christians, played out in front of non-Christians, often leads more to, what appears to be folly, rather than constructive dialog.
I know I have personally wavered throughout my Christian life and in studies as to what I accepted as doctrine and what I believed that Scriptures reinforced and taught. Often times I find that even those who argue and debate the issue actually believe much the same thing but differ only in one narrow area. By this I mean the thought of losing one's salvation. Most Christians do not believe that Satan or another person can rob a true Christian of their Salvation or that a person's salvation can be taken from outside.
The real point of contention therefore, as I have observed it, is whether the Christian themselves can reach a point that they make a determined decision to renounce Christ and their decision. That is usually the primary point of contention. Those who advocate that a person can renounce their Salvation and leave God or reject God ,once they have met and been saved, will then cite the act itself, or rejecting God, as blasphemy of the Holy Spirit, given that it is the Holy Spirit that God uses to communicate with humankind. These are not the only differences in this discussion and doctrinal differences and beliefs how a person can lose salvation, if possible, but I believe they are the main ones in most cases.
For those who advocate OSAS doctrine the choice of those words often portray, to other Christians, that we believe in an insurance policy that permits the Christian to sin and continue to sin as they wish without regard for the Holy Spirit or Christ Sacrifice on the Cross or God's Will.
I personally believe this is a valid doctrine to discuss and debate among Christian believers but not to the point that the Cause of Christ is harmed or damaged. I do not believe this is a profitable discussion to have with persons that are admittingly not Christians or non-believers but that is just my personal opinion. I personally, therefore, believe that this discussion, on this particular topic, is most wisely handled and addressed in Personal Dialogs among fellow professing Christians that desire to participate in such a discussion. Just my personal opinion but regardless suggest for the sake of Christian unity that we keep it respectful, presenting our respective positions and allowing God's Holy Spirit to minister to the hearts and minds and confirm God's truth regarding this doctrine.