from wikipedia. Matches what I understand. So, not originating in a slum then.
It is mentioned as a possibility, not a fact(as you originally stated it)
I'm not sure why that means that the possible effects of colonialism on disease shouldn't be discussed.
It's obvious, isn't it? When you discuss public health issues it quickly becomes apparent that your own good health isn't just a result of individual choices, a large amount depends on the environment, that is on politics. That's a dangerous path that leads directly to questioning the status quo, and the political elites that profit from it can't have that.
When someone like a colonialist wants to introduce the market economy to an area organized into traditional societies, he has to first undermine and destroy those societies, so their people have no choice but to participate in his market as a laborer or else starve.
A really good book on this is by Steven Pinker from Harvard https://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Natur...
The claims are ignorant of actual the colonial processes, history, and economic earlier resource extractive/cash crop and early how industrialization actually works including a conflation of market economy with enclosure of the commons or control of the food supply to remove subsistence options.