Ouch...
The Dutch tax office uses an "expected return" on your investments. This expected return is now 4% annually (Will change slightly in the future to a sliding scale depending on how much you have). This 4%, which they say is the profit you made over your investments, is then taxed for 30%.
The only thing that matters is the value on January 1, it doesn't matter how much it was worth on December 31 of that year, they assume you made 4%. It doesn't matter if you gained or lost money, it simply is 4%.
So what happens if your return is far over the 4% mark? Do you have to declare all of your holdings beforehand and you're taxed on them even if you don't cash them out?
Personally I'm fine with capital gains. It's far better to tax idle profit than everyone's day to day necessities.
It really means you pay 30% over the 4% gains, effectifly 1.2% over your capital. ie 1200 for 100K total capital per year.