If these worlds had biomes it would be imoral to colonize, because for the indigenous population already living there our arriving could mean a world-ending event for them. We have to be very careful these are sterile worlds before sending missions.
Do you feel the same way about human colonization outside of Africa?
We have no idea how two entirely different biologies would interact, if they would at all. Its something that we should study before jumping in head first, but to think that we would travel light-years but not consider the implications is a little preposterous.