The existence of the monarchy is often simply considered to be a quaint tourist attraction, but it has real constitutional consequences. Sovereignty is often said to reside in Parliament, but that is intellectual laziness. The sovereignty of the United Kingdom resides in “the Crown in Parliament”.
There is not US-style separation of powers in Britain. The supreme judicial function used to reside with the Law Lords sitting on the wool sack, who would sit in the House of Lords alongside all the other hereditary and non-hereditary aristocracy. The analogous position would be for Roberts, Ginsberg, Kavanaugh et al to be sitting senators with a vote on legislation in addition to being judges ruling on cases brought before them regarding that legislation. The Law Lords were replaced with a Supreme Court by Tony Blair and Gordon Brown, who also excluded the hereditary aristocracy.
The hereditary aristocracy functioned to represent interests in a similar way to US senators prior to the 17th amendment. By allowing only the non-hereditary aristocracy to vote in the House of Lords, Blair turned the chamber into a pension system for failed elected politicians and government flunkies that carried water for the establishment.
Imagine Lord Eric Cantor, Lord John Boehner, Lord Paul Ryan, Lord Eric Holder, Lady Lois Lerner, and the future Lord Robert Mueller being appointed senators for life after they had been removed from their previous positions.
Fortunately, the Parliament Act of 1949 precludes the House of Lords from preventing the passage of budget legislation and also enables the House of Commons to force the passage of legislation in support of the official manifesto upon which the governing party was elected.
And so on at the end of the link.