"Wiped out" is a continuum
When an advanced civilization encounters a less-advanced civilization, the latter is "wiped out", sort of. In human history, most less-advanced civilizations are assimilated, not totally destroyed. The extent to which a less-advanced civilization contributes to the more-advanced civilization is roughly in proportion to the unique "useful" features of the less-advanced civilization. Why is this a problem? If you are worried about your biological progeny instead of your intellectual progeny, you should be worried much more about the technological singularity or various existential risks instead of worrying about ETs.