Yes, a country should colonize another country, because wanting to expand is a natural thing among humans. People move to other countries and places all the time. They have throughout human history. It is okay if people want to move to another place and set up their own government, as long as they don't hurt other people.
The US is probably one of the biggest colonized countries in the world. Of course colonization can only really happen in countries where people are free to come and go and opportunities exist. Intentional or organic colonization can be useful for expanded learning among people of different backgrounds. It can create a melting pot of new ideas and a better life for all.