Smallpox Blanket Meaning

Example : 1998 May–Jun, Matsen, Bradford, “Travel to exotic foreign lands! See beautiful coral reefs! And kill them!”[1], Mother Jones Magazine, volume 23, number 3, : Foundation for National Progress, ISSN 0362-8841, page 67:  The irony is that barely two decades into Jamaica's boom time, the country's reliance on tourism can be compared to a smallpox blanket: It'll keep you warm for a couple of nights but kill you in the long run.