Tourism has its own negative externalities (i.e. it’s own kind of “polution”) that negativelly affect the rest of the Economy if it gets too much and might even kill the very things which attract tourists. This is generally manifested as a rising cost of housing and general cost of living in touristic areas which pushes out the local residents and businesses.

Also tourism doesn’t employ highly qualified people, but rather people with basic education.

So it’s only good for economies up to a certain level of tourism and how much that is depends on how much that’s a high value added Economy (roughly, how wealthy and developed a nation is) - much higher levels of Tourism are still a good thing in, say, a mid-development level Economy with basic universal education where before Tourism most people worked in the Primary sector, than they are in an Economy of high value added industries employing higly qualified people: a country can have an Economy where Tourism is a high percentage to pull itself up to about the level of the poorer European countries, but no matter how much you have of it Tourism will never turn a country into a high tech powerhouse, beyond a certain point quite the contrary (not least because high costs of living due to it kill starting companies, even high tech ones, because they make the costs of business go up at multiple levels).

A bit of Tourism can be a good thing, a lot of Tourism is only a good thing if the alternative was an economy of mostly Primary sector activities.