Regardless of the situation, capital punishment is the intentional killing of a human being, which is murder, government-sponsored murder at that. In addition, Anne Boelyn didn't do anything close to what would be considered a capital crime - she didn't kill anyone or even try to do so, therefore regardless of ones position on capital punishment, she should not have been beheaded.
Anne Boleyn was a victim of the political arena in which she lived. She was only accused of adultery and beheaded because Henry VIII wanted to marry Jane Seymour because Anne had not yet given birth to a son. Capital punishment was used loosely in Tudor England and by today's standards Anne wouldn't even have committed a crime, much less one which she should have died for.