To the contrary, there might be an evolutionary benefit in having your parents die off shortly after they've done all they can to increase your, and your siblings, chance of reproducing. The reason a timely death might increase the chance of the gene-line's survival is because the parent might otherwise consume scarce resources that are better invested in the offspring.
All that evolution "care about" are genes, no individuals. That doesn't mean that sometimes big life-span of individuals can't be a good strategy for some genes.
About the down-voting thing: it seems to me that if you disagree with somebody, instead of down voting, the best strategy is to answer.
If you don't care enough about the comment for answering maybe you shouldn't be down-voting.
In my opinion, down-voting should be use for keeping the conversation civil and on the subject at hand, or things like fighting spam, not for expressing disagreement.
It doesn't look like a rule that makes the conversation more interesting, though.