> There's plenty of empirical evidence to indicate that language influences thought, and that syntax is therefore important.

Are you talking about natural languages here? The so called Sapir Whorf thesis - in its strong or weak form - is rather controversial. There are some interesting findings, but the interpretation of them is still hotly debated.

In any case, none of the studies that I've seen (e.g. about colour perception, spatial reasoning, etc.) seem to be about syntax. I'd have to see some evidence that head-marking language speaker somehow think differently than dependent-marking language speakers and I haven't seen that.

> your argument ad absurdum is generally reasonable

it's a valid argument when somebody is speaking in absolutes, but I haven't seen GGP do that. There's a difference between saying "all syntax is completely arbitrary" and "syntax is not the point" - the latter suggests to me that if you stay within certain reasonable bounds (e.g. not be whitespace or malbolge), whether you use significant whitespace of braces, the language looks more like Pascal or like C, etc. are of minor importance in the grand scheme of things. Which is something you may disagree with, but it's a much more reasonable point that anything you can just counter with "but whitspace!".