Thinking of immigration, population growth and so forth; how we accommodate people in society makes a big difference. Some of it is attitude. Standing in a line waiting for something, like at the Post Office, presents an example of of this. If there's lots of people in line, it can be bad if one is in a hurry and doesn't want to visit with anyone in the line around them. On the other hand, a long line can be a pleasure if one is enjoying conversation with the people around them. I've been in lines where I'm sad when I get up to the window as that means an interesting conversation with a neighbor in line ends. Other times, when I haven't known anyone in the line or had reason to strike up conversation with strangers, the long line can be tedious and unpleasant.
More people can be good if it means more customers for your business, unless you can't keep up with demand or want a slow day for rest. More people can be bad if you've worked hard to buy a house with a private swimming pool and the growing population has depleted local water resources to the point where it's now illegal to fill and use your pool.
More young people can be a blessing for paying into Social Security.
A curse if there's a housing shortage.
A blessing if one wants diversity of ethnic food restaurants around to sample.
A curse if one is stuck in traffic due to more sprawl.
A blessing if one wants light rail in their city since light rail tends to require density to be viable.
Attitude and how we plan our living environments, after the people arrive, makes a big difference.