1. Some intelligent design is actual - this post, the computer it's written on, the monitor I'm looking at, etc. They are, in whole or in part, indisputably designed by a mind.
2. It's logically possible, however, for some things to be utterly undesigned - some events or structures are not foreseen, created or pre-ordained by any mind.
3. It's also logically possible that all things and events are ultimately designed, either in whole or in part.
4. I have indisputable evidence that design is responsible for at least some things or events, via 1.
5. I have absolutely no indisputable evidence for the utter/complete lack of design with regards to any object or events.
6. Logically, on these terms alone, if I make any inference in either direction, reason and experience favors 'design' as my default assumption.
This is a rough argument, and it is weak in terms of what it gets. Hume can be deployed easily to argue this doesn't get me to God, or at least not the God of any revealed religion. It doesn't get me to classical theism - or even monotheism.
Maybe there are multiple designers. Maybe the designers are all dead. Maybe they're mad, maybe they're evil, maybe they're stupid, maybe a lot of things. Maybe there are even no designers at all (at least not in the 'large scale' sense), and the inference is mistaken. This is not an argument most theists would feel comfortable deploying, because it kicks open the door way, way too wide. They'd want to immediately march on and do more work, or drop the argument altogether in favor of another one that demonstrates rather than infers, and demonstrates God rather than a designer.
I respect that. But I still subscribe to this argument, and I deploy versions of it in discussion, because - as near as I can tell - it's sensible, and it still demonstrates something important about the default state of our experience of the world.