While I certainly agree that nothing can be proven to another and only that which we experience do we usually accept as true reality. The problem is that most people think in terms of the deductive true or false dichotomy, and that’s not the way the world works. Rather, we have to think and live in terms of probabilities. Gravity may not always be the case, but I operate in my everyday life as it it’s functioning, and so far my behavior has worked for me. Although that’s an extreme example, it illustrates the idea. While I can’t disprove the existence of any god, similarly, I can’t demonstrate its existence. Further, I can’t find any situation where the existence or the effect of any god has been shown. As such, introduction of such a concept just adds unnecessary and often destructive complications.
While they may introduce all sorts of philosophical ideas, it would seem to me that a weakness in their argument is whether they can demonstrate where not applying any of them will cause me to be less effective in my behavior.
This may not respond to all of presupposition, but does it apply at all?
I can think of ways that a skilled presuppositional apologist would answer your objection, but I’d rather not get into that. If I answer objections like this to show that there is more to presuppositional apologetics than it seems on the surface, then I will be put in the position of defending it. And then I will look to everyone like I am one of them. That’s how the fighting and bitterness started at other atheist sites.
If this is something you’re interested in, I can post links for you to the best resources on the internet for what it’s all about. That would be better than trying to talk to apologists themselves, because a lot of the mechanics behind this method are usually left out of discussions and debates.