There are also huge — albeit fairly improbable — disastrous consequences to voting 3rd party. For example, if Romney loses VA by fewer votes than Virgil garners, and the Marxist wins another four years as a result, that would also be “non-negligible,” to say the least!
Those who harp on those voting third party seem to make the same assumption: if they do not vote third party, they will vote for Romney. There are other possibilities, most likely not voting on that line at all. Not everyone believes Romney has changed his views as radically as he claims. It is hard for some to pull the lever for someone whose history is opposed to their views.