As a population biologist I believe I can speak to this. Humanity is more genetically diverse, in terms of persistent polymorphism than any other mammal by an order of magnitude. Furthermore, the population is growing and globally mixing, so positive selection dominates drift which means that mutations will tend to stick around until election can act on them. Each day about 350,000 children are born with a mutation rate of 10^-9 per nucleotide and 3^9 nucleotides per genome, Each day 175,000 new mutations appear in our gene pool. I think we'll be ok.

Interesting fact: There is more 'Fossil' retrovirus DNA in our genome than Protein Coding DNA http://www.newyorker.com/reporting/2007/12/03/071203fa_fact_specter. Retrovirus infection is nothing new to metazoans, and the typical cycle of integration is infection, spread, mutual tolerance, and eventually conversion to transposable elements. There is strong evolutionary pressure on HIV to follow this pattern, if for no other reason than a healthy carrier spreads the virus faster than a sick one.