I understand the idea behind the defenseless receiver rule, but the worst part about this fine is that Whitner was coming in with his shoulder and Givens rotated over and down after Whitner appears to be committing to the hit. If Givens falls down on his back, instead of toward his left side, Whitner's hit is directly into his shoulder, not his head/neck region. It strikes me as patently unfair given just how body motion works in this case.
Whitner is not taking this lying down, as he indicated late last week that he would appeal any fine. Additionally, he is drumming up support on Twitter, working up a t-shirt that will say #LegalHitner.
I'll post a link when the t-shirts are available for sale. Hopefully the NFL sees the light on appeal. I'm not holding my breath about that, but you never know.