Originally Posted by
NickB
If, as you suggest, the blank page is not officially required if you already have your visa, then as long as you had proper documentation and presented yourself at check-in at least by the check-in deadline specified in your itinerary/communication from the airline or travel agent (or, if no such deadline was specified at least 45 minutes before departure), and were refused boarding, you have been involuntarily denied boarding within the meaning of Regulation 261/2004 and are therefore eligible for compensation.
There are a lot of IFs in your post. irishguy in the previous post cites the State Dept that at least one completely blank visa page is required prior to entering the country. Playing semantics with this as the OP did - I already got my visa, so I really don't need that much extra space except for stamps is not going to fall on sympathetic ears with KLM.
I would not consider flying anywhere with a half free page in my passport even to a visa-free or visa-on-arrival country unless it's an emergency, which I'm not sure this is.
OP, since you're such an expert on space - leave just one corner of a page empty in your passport and advise the immigration officers at port of entry how to place the stamp in your passport as to fit in it.