That's the same reason why there would never be an organism to evolve further than humans. Humans would just use technology to destroy anything that becomes a threat (after all, we compete for the same resources).
Let us assume so.
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Well, we can hope so. My concern for the future is some sort of antibiotic-resist disease that very well could wipe out humanity if pathogenic enough with high transmission. With viral infections, the transmission and virulence relationship can be complicated, because viruses need hosts to replicate, and so keeping the host alive is within the interest of the virus. With bacteria or some sort of fungi, they can self sustain without a host.
I interpreted the poster to be referring to some sort of primitive organism that might out evolve humans, but I suppose an existing pathogenic organism could enter the gradations of evolution and become a super bug that wipes out humanity.