What does criticism of our recent history have to do with the cross? Probably closer to the intent of the question would be, How can you say such negative things at the foot of the cross?

The Cross represents forgiveness. In one sacrifice for all time, the penalty for sin was paid in full. The priest no longer had to offer sacrifices to cover the sin of the people, Jesus provided atonement once for all. (Hebrews 9:24-28) The connection between God and man was no longer through a caste of men serving as mediators, the connection was direct to the throne of God, himself.