In what other circumstances is it, not merely OK, but obligatory, to do what we think is a little evil (or not wrong at all, even though centuries of moral theology says it is an objective evil) to advance what we believe to be the greater good?If you look at the bit I have emphasized you'll see the issue. If something is an objective evil it raises the bar quite a bit about what circumstances it is acceptable to lie. For no matter how good your reasons for not telling the truth, you will be doing some evil.
On the basis of this argument, you might lie to save someone's life but you should still go to confession the next day to get absolution for telling the lie.
Suppose an armed gunman came in and said he was looking for Cecilia and you knew the woman sitting on the park bench was in fact Cecilia but told the gunman, "I don't know Cecilia but that is my friend Nancy." On the metaphysical definition you might be able to justify the lie but it would still be an evil. So you would go to the confessional, get down on your knees and say, yesterday I told a lie.
What should we do about such an argument?
That's easy. Ignore it. You couldn't possibly reason with a person who believes such a thing.
It's not that they are irrational. Go read the rest of Bender's argument and you will see that it is quite rational and there are even some good lessons to draw from it. But the notion that something might be an objective evil is not one of them. This isn't an argument but a move to shut down argument and it deserves to be ignored.