I would say choice is always the better option, people just work better mentally when they feel that they have some control over their actions. This probably explains why the people in the story who become infected by ALAS try to become more altruistic outside of the blood-giving, so that they can tell themselves a story about their choices, and then maybe not feel so alarmed by their sudden need to give. That said, I would personally be very tempted to take Les' view and let the virus spread, because people are jerks and could use a hand in being kinder to their fellow humans. And now I am not sure how I feel about my desire to turn people into puppets even if it is 'for the greater good.'
I agree with you. To me, the basis of being a person is being able to choose and not being a slave to instinct. Further, I think life is a whole lot easier to deal with when you get to make your own choices and forge your own purpose. That being said, people are far from ideal and some will choose poorly. But I still think they shouldn't be forced to choose better, because who can objectively say what 'better' is?