This isn't an argument for good or bad, but America was founded by immigrants and they've continued to arrive and build the country ever since 1776. If you think the American state is a good thing, it seems reasonable to favor immigration.
Personally, I believe that no human is fundamentally better than another and that we don't own the planet but merely inhabit it. This means I also believe we all deserve to be treated as equal citizens of a global nation. I realize that in practice you can't just dissolve all the borders at once, but nevertheless less restrictive border controls which includes things like increased immigration push things towards that ideal.
Personally, I believe that no human is fundamentally better than another and that we don't own the planet but merely inhabit it. This means I also believe we all deserve to be treated as equal citizens of a global nation. I realize that in practice you can't just dissolve all the borders at once, but nevertheless less restrictive border controls which includes things like increased immigration push things towards that ideal.