A government with common sense.

Traveling to the DPRK is bad because:

1) It provides funding to a vicious totalitarian government which is working 24/7 not only to oppress their own people, but also to develop WMDs for the purpose of extortion and/or actual use against the RoK, Australia, Japan, and the US.

2) It provides an opportunity for the DPRK to take Americans hostage on trumped up charges and use them as bargaining chips.  Currently, at least 4 Americans are being held in the DPRK.  Many American hostages have been used in the past to extract concessions from the US in negotiations.

3) As the case of Otto Warmbier shows, travel to the DPRK can get a nice American kid murdered.

4) Tensions are high in Korea;  few would be surprised if war broke out.  Being an American tourist in the DPRK if there is war could be fatal.

The DPRK is a dystopian, tyrannical regime that should be cut off from civilized countries and not propped up with $$$ from a country it wants to destroy.