As someone with a strong belief in the rights of indigenous peoples, I've always felt that it was not immoral for the Europeans to bring smallpox to America, given their ignorance of germ theory, among other things, but not showing sympathy for this accidental apocalypse, and aiming to either mitigate it or adopt policy with a tone of compassionate consideration to be reprehensible.
But that's easy to say with hindsight and knowledge of smallpox viruses. I've read estimates that up to 90% of Native Americans died to disease that spread faster than Europeans could travel, meaning what they explored was post apocalyptic. Even without germ theory, were there contemporary accounts acknowledging this?
They realised quite early on (about 1525) that they had brought doom to the natives via sickness, though the did not know how the transmission worked. I answered a similar question a year ago, and I think my answer will be useful to you:
https://www.reddit.com/r/AskHistorians/comments/myikzc/comment/gvwovht/
Most historians no longer believe that 90% of Native Americans died to disease before Europeans arrived. See this answer by u/p4quime_fan addressing the state of historical consensus on disease spread in the early colonial Americas. In general, most excess deaths were directly or indirectly caused by colonialism, whether through enslavement, warfare, or loss of land (each of which contributed to disease mortality).