If you read Mr Corbyn's statement fully, it gives context to his observation that Bin Laden's death is a 'tragedy'.
He is not saying that the loss of Mr Bin Laden is a 'tragedy' as such, he is referring to it as one more tragedy in a series, and that is something entirely different.
Mr Corbyn also qualifies his point that Mr Bin Laden's death, as opposed to a legal trial, will be seen simply as an assassination by Mr Bin Laden's supporters, which will lead to additional unrest.
On that basis, I have no issue with Mr Corbyn's point f view.