David,
As Paul says, there are a number of environmental success stories in the UK, including links courses, where the club, course and environment (and its support groups) are able to work together. A shame that's not the same in Holland? Having said that perhaps with time it can change? Some years ago most people in the UK would have said that golf was bad for the environment, but thanks to a number of factors such as wildlife programs like Springwatch showing how good courses are for wildlife, people are starting to change their short sighted opinions.
I do understand your frustration, especially as you had previously approval for the work, but are you sure the snails are meaningless? I'm no expert on the ecology of dutch dunes but there are any number of reasons why the snails could be important to the food chain or biodiversity of the area? From everything you have said, your frustration should be targeted at the protesters, not the things that they are claiming to protect.
Cheers,
James