What is the purpose of a life or a country? To maximize wealth or to maximize utility?

Summary from an article written in the context of Brexit.

1. There is good evidence that immigration is good for the economy.

2. But there is nothing which states that maximizing wealth is the purpose in life.

3. Even economists don't insist that personal wealth maximization is the goal - it's utility maximization which is.

(And if Britons insist that not having 5 million immigrants increases utility, that's upto them. Utility function after all are entirely personal.)
Note: 5 million is a very large number, do these people have to leave Britain on Brexit date?

Soucre: http://www.forbes.com/sites/timworstall/2016/10/10/the-brexit-conundrum-freedom-of-movement-means-only-hard-or-clean-brexit-is-possible/#48cc5b5ffd71