You are making a dumb conclusion with absolutely no proof what so ever.
Your dumb as a rock conclusion is as follows: Three practicing Catholics uphold capital punishment, and so a fourth practicing Catholic will not let his Catholicism influence his judgment with regard to capital punishment.
Dumb, dumb, dumb.
My only remark was that: maybe he will emerge as an opponent of capital punishment, and if he did that would be consistent with his Roman Catholic faith (whether or not due to that reason), which was held by many to be a positive factor.
PS. And it's worth noting that I oppose capital punishment, so it would hardly upset me if Alito were to emerge as an opponent of the death penalty. My views on both abortion and the death penalty are almost entirely consistent with the Catholic Church, more so than that of many American Catholics, and I'm not merely a lapsed Catholic, I'm a collapsed Catholic. LOL