No, you are wrong in that line of thinking. The weather forecast published by the KNMI was sufficiently pessimistic to justify cancellation. A front is forecast for tonight with thunderstorms, continuing on into tomorrow. As an organiser you have to consider the cost of not cancelling and a low turnout. I was talking to the organisers at the beginning of the week and they were agonising over the decision then. It is not just a question of people not turning up. Guest speakers need to be confirmed/cancelled, likewise catering and airport staffing.
I don’t disagree with those reasons. It is a bit like if you are doing a trip with someone who says to you “I must be back at work on the Monday or I will be fired”. Such a trip must be cancelled unless the forecast is absolutely solidly CAVOK. In fact I would say one should never fly with such a passenger.
The obvious problem is: no forecast of “absolutely solidly CAVOK” can be relied on 4-5 days ahead.
I can see if you are also dealing with trade exhibitors, that is an additional issue.
But then how does any GA retail+trade show manage to run? Can they get insurance based on a specific wx forecast?
A standard exhibiton would not need insurance as people have the option of driving. In the case of Texel, being an island, this presents problems so car and ferry for a couple of lectures and a barbecue – turn out zero.
OK let’s do another “class” 
An assessment of EGKA-LDLO on 26th August, EOBT 0700 UTC.
Windy.com 0700 UTC
1200UTC:
I reckon Texel were right to cancel
METAR wind 320° @ 11 kt, Temp 16° / 10°, 68 %, Pressure 1009 hPa , Visibility 9999 m, Cloud Few Cumulonimbus at 2.200 ft, Recent Drizzle
TAF for De Kooy (EHKD) 25 aug 2018 09:00 Z – 21:00 Z
Updated 1 hr 45 m ago
Wind 310° @ 10 kt G 20 kt, Visibility 9999 m, Cloud Scattered at 4.500 ft, Occasional 09:00 Z – 21:00 Z
Wind 310° @ 13 kt G 25 kt, Cloud Scattered at 1.500 ft, Scattered Cumulonimbus at 2.200 ft, Broken at 3.000 ft
Occasional 10:00 Z – 17:00 Z (30% chance), Wind 320° @ 18 kt G 30 kt, Visibility 4000 m, Cloud Scattered at 1.000 ft, Scattered Cumulonimbus at 1.800 ft, Broken at 2.500 ft, Thunderstorm, Rain
As a VFR flyer I reckon your flight is a no-go – certainly north Italy. Western med does not look to clever either.
As it turned out, the whole flight was in VMC. Departure 0800Z from EGKA, landing on LDLO 5hrs later, in 4km vis, light rain but very strong winds (60-70kt at say 100ft, 40kt on the surface) albeit almost lined up with the runway. FL100 until 50nm before the Alps, then climbing to FL170. Should have departed 2hrs later because LDLO cleared up rapidly then But the UK end would have been bad (not hazardous in terms of CBs but IMC and probably icing).
The Autorouter Gramet was fiction at the destination end
but the Gramet from OGIMET showed it right
This is the wx over N Italy and the Pula region
