I want to return to the OP and the heart of the “argument.”
You’ve worked hard, @Vinnie, to support this strategy as well as Christian thinkers who have proposed it in an attempt to explain that there is reason to believe that God has made us for his purposes. I am not a logician, philosopher or apologist; so I won’t speak about the topic as they do. I am, however, a Christian. Yet, I find the attempt to use human desires an inadequate argument for faith outside of faith.
I think, most simply, it relies on unprovable contingencies, too many “If-then” statements. In the end, we are left with no more than If-Then.
It relies on fuzzy definitions or concepts – particularly “religious desires” or even “desires.” There are many things that could be classified as “religious desires” which Christians would see as such, but which can be seen in other ways as well. They can indicate a great many things
It relies on theological assumptions and explanations, when others are adequate.
As I’ve seen discussed here, it demands a system of classification of desires in order to negate valid objections to what is stated. This feels like the rules of the game are being defined as we go in order to benefit the house.
You asked about benefit of the doubt. I think this might matter most and beyond the scope of the discussion of Lewis’ argument from desire. If an apologetic argument is intended to provide a convincing explanation or defense of the faith, it needs to do that without the benefit of the doubt. Allowing someone to make their argument is one thing. Requiring the hearer to give the benefit of the doubt is another. If the hearer is unconvinced, or sees and identifies all sorts of logical problems, why keep hammering on defending the argument? The argument is not the point.
Moving even farther from Lewis’ argument, and to the topic of the related thread (Is apologetics (often) a waste of time), I want to address what is for me a serious problem with argument-focused apologetics. As I see them here and elsewhere, eventually they focus on the argument, logic, strategy, rules of argumentation. In doing that, I find that rather than building faith, they build resistance to faith.
I see this in myself, and I see it in the threads as well. I’ve experienced it with formal apologetic arguments I’ve heard from other christians and even from elders at church. When I am confronted with a statement like the OP, which logically tastes off to me, I immediately start trying to understand why. Even if I can’t articulate in formal terms of logic, I can understand for myself, what the problem is.
By the end of the process, there is one less reason to believe.