I don't disagree with you there. I see the law happening only only withstanding until the next election period and the people realize they want their tourists back. It's going to take some time for the tourist trade to peter off though as many probably wont know about the law change. If anything, this will be a 4 year trial period and the they'll be begging for the tourists to come back---so they'll reintroduce the law but with some added restrictions because they won't want to admit they were entirely wrong.
And honestly, why else go to the netherlands? The city of Amsterdam isn't that beautiful if you take away the drugs. You got so many other fun places to go: Heidleburg, Belgium, Paris, Prague, Barcelona, London, Munich.....The list is endless. Many tourists will find their money better spent in other cities that have better culture, cuisine, architecture, and beer (people don't travel half way around the world for a Heiniken --I barely go across the bar for one).