Haimy – there are two points here:
1) What is the ultimate Emess which will be reflected in Hashem’s judgement of the OTD person and everyone who had any effect on them
2) What is a helpful attitude to have to help these kids and try to prevent it happening.
You are right as far as point 1 is concerned. However point 1 is something we must remember and tremble and do teshuva for our own aveiros and not blame them on the effect others have had on us. Practically however, the accepted mehalech is that pointing out and (over)emphasising the shortcomings of the parents/teachers etc of the OTD person, while unpleasant for them, makes the OTD person more likely to return, and puts a greater responsibility on those parents/teachers etc to prevent it from happening.
(I think this is what DaasYochid meant “How does that change how we deal with it?”).