My mom and I just came back from Lisbon and we argued all week over whether the tourist crowds ruin the city or actually keep it alive. She couldn't stand the packed tram 28 and the souvenir shops replacing local bakeries, while I kept thinking about the 70% of jobs in the old town that now depend on visitors. Can tourism really coexist with local life, or is every beautiful city destined to become a theme park of itself?