I meant to say that the need for accuracy is even higher for the laminar flow sections as compared to non-laminar sections. So it makes them harder to build, yes. Unless you have access to a CNC mill. Point I am trying to stress is that hand building foils to a sectional shape like e.g. the NACA series is very hard if you are aiming at a concrete set of properties in the finished product.
Getting down to 0.5mm with a hand plane and belt sander, while keeping the foil straight lengthwise, is pretty well done in my experience. I tried my hand at a couple of ply/glass foils some time ago, and it was tedious work ending in a not too good result. I liked Phill Branders method better, where he made a outline of the section he wanted and glued sandpaper to it. Then proceeded shaping foam with this "jig", before laminating carbon to it and glueing the halves together. He used to have some photos of the process on his website (which have disappeared due to changes the web provider did).