So, what is so controversial about it?

Ok, of those who have seen the alternate ending to I Am Legend, it is suppose to be controversial. I have watched it several times and I don't see what is so controversial about it. So, if you have seen it and know, tell me. If not, the link is below. Discuss!

I Am Legend Alternate Ending

The recent thread we have about it covers that discussion fairly well, since people seem to disagree over the quality of both endings.