The problem is the kid feeling left out at school when they're the only one without a smartphone and can't participate in their friends' activities.
Moreover just because that laws and regulations are applied inconsistently in the US (and we are talking about Denmark here), does not mean we should completely do away with them.
I highly recommend discussing a smartphone pact such as http://waituntil8th.org with fellow parents before anyone in their friend group gets a cell phone.
Do parents actually fall for this drivel?