We aren't bacteria, viruses or parasites. We are like all other lifeforms in that our natural tendency is to reporduce and expand to fill our environment to the extent possible. One difference is that we have a much greater capacity to change our environment than other creatures do, and we have no natural barriers to our expansion, so we have a great capacity to cause harm to our environment and other creatures that share it. The other crucial difference is that we have a capacity to recognize that problem and do something about it. Bacteria, viruses and parasites cannot do that --- they often kill their hosts. Hopefully we are enough different that we will not kill our host.