Kasab should be allowed to live -- in prison, for life.
At Have You Heard, Ayeshea Perera offers what I think is a compelling reason (this is also Joseph's reason):
I believe that by killing Kasab you are making him a martyr – and then in some sordid twisted way, he wins. Kasab was sent here on a suicide mission. It was just his bad luck and sheer circumstance that saw him captured alive. He came to Mumabi fully prepared to die – to become a martyr. But by keeping him alive and in prison, he has been denied this ‘final glory’.
In the midst of all this sordidness, The Daily Tamasha manages to keep its funny neurons alive: Nation Shocked As Suhel Seth Has ‘No Comments’ On Kasab Verdict. [In case you need a refresher course on Suhel Seth, read this post by Girish Shahane].