I do not think it possible that the legalization likely to affect all those negative aspects, are certainly influenced by other causes! If in Italy you find weeds with seeds was Albanian, in the city centers are just crap or this or poor Moroccan hash. There are mainly three deliveries in Italy as Albanian sucks, the Spanish good and the most difficult to find the Italian which is better than the Dutch. For this reason legalization would lead people to smoke at least healthier and not that crap cut or soaked with everything.