This is a common fear in a lot of western countries. I really would like to see numbers on how many fake marriages have actually been avoided by the drastic policies in place, and see how that compares to the cost of enacting these policies.
I am in a relationship with a foreigner (Chinese) in a country that has very strict laws on spousal visa (France). I dread the moment after we get married when we have to go through the whole process of the government checking if this is a real marriage...
The problem with immigration reform is that the effects are very long term whereas politics operates on the 4-year electoral cycle. When it comes down to Denmark's basic problems with non-assimilating immigrants, you won't be able to see clear effects, beneficial or otherwise, until a full generation and a half has passed. But everyone wants to take credit here and now for what progress has been made since the last one or two elections while blaming the opposition for stagnancy or regressive tendencies.
In the areas you mentioned, I wouldn't be so quick to jump to easy conclusions about cause and effect. How much of the effect is due to Muslim women, many now third generation, having become more assimilated than their male counterparts, and so that's the larger part of the explanation for why they are entering higher education in increasing numbers? Besides, this fits the general emerging pattern in the modern world of male vs female skew in higher education.
I'm sure the 24-year rule had some positive effect. How much isn't clear, and it would have to be weighed against its negative effects, equally hard to measure.
I am in a relationship with a foreigner (Chinese) in a country that has very strict laws on spousal visa (France). I dread the moment after we get married when we have to go through the whole process of the government checking if this is a real marriage...