It should upset you if you're a consistent conservative. The Constitution clearly provides for capital punishment. Any decision to the contrary -- whether based on changing societal values, norms of international law or religious beliefs -- simply constitutes a justice substituting his view of what constitutes "good" for the clear guidance of our adopted Constitution. If a justice wants to say the death penalty is unconstitutional, he should have run for elective office.
Impeach Alito!
That's it. And there is absolutely no way to apply the Eighth Amendment except by subjective measures. The Constitution does not define "excessive bail" or "excessive fines" or "cruel and unusual punishments" at all. It is left entirely up to the subjective judgment of the individual. It is easily the most subjective clause of the entire Constitution.
And no one can deny that notions of what constitutes "cruel and unusual" punishment have changed over the centuries, and will continue to change.
The Constitution deliberately contains terminology which is intended to be a mirror on current mores.