Others have cited Guns, Germs and Steel but I hope I don't have to explain that its premises have in many parts been debunked by actual historians who specialize in these subjects.
It's easy to forget that most of the Indigenous peoples in North America didn't die simply from "catching" diseases but were directly and intentionally killed or worked to death. Most people are hopefully familiar with the extent of the genocide in what is now the US (with everything from "plague blankets" to eradicating the bison to literally paying bounties for dead Indians) but Columbus' treatment of the Natives was also so violent and brutal that other Spanish colonialists complained about it.
In other words, the problem wasn't so much settlers bringing their diseases with them than settlers capturing the natives, working them to death, destroying their livelihoods and then actively trying to genocide them.
Having some level of immunity to smallpox or other diseases wouldn't have changed much.
It's easy to forget that most of the Indigenous peoples in North America didn't die simply from "catching" diseases but were directly and intentionally killed or worked to death. Most people are hopefully familiar with the extent of the genocide in what is now the US (with everything from "plague blankets" to eradicating the bison to literally paying bounties for dead Indians) but Columbus' treatment of the Natives was also so violent and brutal that other Spanish colonialists complained about it.
In other words, the problem wasn't so much settlers bringing their diseases with them than settlers capturing the natives, working them to death, destroying their livelihoods and then actively trying to genocide them.
Having some level of immunity to smallpox or other diseases wouldn't have changed much.