I'll go with BasilY's summation, as it reflects my own feelings on the subject. If he did it because he thought he was protecting himself by sinking debris, and not from willful murder, then he deserved prison time for being stupid if nothing else; but the death penalty was a bit extreme under the circumstances.
The account of the trial itself is fascinating, and I had not read it before, even though I am a regular visitor to
www.uboat.net. Thanks for the reference.