Chief Justice John Roberts, seen here in 2013, is not happy about the court legalizing same-sex marriage. (Win McNamee/Getty Images)

Today's Supreme Court decision legalizing same-sex marriage in all 50 states completely undermines America's democratic process.

That's the bold statement Chief Justice John Roberts made in his principal dissent. In one day, Roberts said, the court has basically transformed the societal institution that has held together humanity for millennia.

"Who do we think we are?" he said.

Here's more  from Roberts's dissent -- something he read for the first time out loud from the bench to signal his strong disagreement with the court's 5-to-4 decision:

Roberts's unequivocal disagreement is somewhat startling, especially as the conservative-leaning justice seemed to be searching for a middle ground just a few months ago during oral arguments on the case, reported The Washington Post's Robert Barnes.

The chief justice has a particular obligation "to try to achieve consensus," Roberts has said.

But Roberts didn't agree with the Supreme Court's 2013 decision to expand federal rights to legally married gay couples. And he made clear Friday that no consensus is worth a decision he feels oversteps the court's constitutional bounds.

Near the end of his 29-page dissent, Roberts registered this strongly worded reprimand:

"If you are among the many Americans -- of whatever sexual orientation -- who favor expanding same-sex marriage, by all means celebrate today's decision. Celebrate the achievement of a desired goal. Celebrate the opportunity for a new expression of commitment to a partner. Celebrate the availability of new benefits. But do not celebrate the Constitution. It had nothing to do with it."

[How each justice came down on same-sex marriage]

The Supreme Court ruled, 5 to 4, that same-sex marriage bans are unconstitutional. Here's what you need to know. (Gillian Brockell/The Washington Post)