There are records of population dying from diseases, but the magnitude was known only recently. And the records they destroyed were mainly Aztec and Inca, which are known as large civilizations, as opposed to the amazonian ones. It’s now that they were nice, it’s that there was no knowledge that there was anything to search. Only the quest for El Dorado counts and has been regarded for the longest time as looking for a fairy tale.
Palestine is not a breakaway region. It has never been recognized as a part of Israel and its people are most definitely not treated as Israelis. This makes the stance on Palestine easier to understand.