I think we are somewhat seeking to squeeze camels through needles, here.
Jordan has a good point, and if I understand it clearly, maybe I can simplify it:
The hardest thing to do with folks today is to convince them they are sinners. yes, the Spirit convicts, but he uses us to convince with words, while He turns the heart. The Commandments, at least the nine that apply in the NT, lays out some very easy to understand concepts of what 'sin' is: Stealing, lying, adultery, et al. It makes concrete the (to the lost) vague concept of 'sin'. And any ONE sin will bring a person to hell, without that sin, and all others, being washed away by the blood of Christ. So, we use the commandments, because they Do describe sin, to show a person that they have sinned, and because they have sinned, they are bound for hell, and rightfully so.
So using the commandments in conjunction with, say, "For all have sinned and come short of the glory of God", shows that 1: we are all sinners, and, 2: because of that we fall short of God's demand of holiness and righteousness, without Christ.
No one is saying that we must all adhere to the commandments and laws-Christ nailed the commandments and law to His cross-but those who are not yet covered by the cross of Christ, as it were, are still lost.
People need to know WHAT sin IS, becfore they can accept that they HAVE sinned and are lost. I believe this is an excellent way to do it. Not always the only way, but definitely one.