Even if we assume that “the billion Euros of cannabis sold there each year” is not a wild overstatement (that’s an unimaginable amount of weed), the Danish GDP

Even if we assume that “the billion Euros of cannabis sold there each year” is not a wild overstatement (that’s an unimaginable amount of weed), the Danish GDP is some 300 billion Euros. As for tourism, it’s just one of a long list of tourist attractions in and around the city. It would not make a huge difference if Christiania disappeared tomorrow (although Christianshavn would be a much nicer place).