I believe GP, myself and everyone else earned our job the hard way. We have never claimed we deserve it, we put in effort, competed in notoriously difficult hiring processes and got selected.
Additionally, our employers have had to provide extensive documentation to the Department of Labor that no US citizen was eligible at the time of hiring - the laws are very strict and comprehensive about this.
We are here, just like every other immigrant, to try and make a better life for ourselves and our families. After living here for 12 years, GP would have been a US citizen if he was born in any other country other than India or China. Unfortunately, being born in India is punished with an estimated[1] 83 years of very limited rights, almost zero liberty (no liberty to produce and publish art works, no liberty to join a band and sing at a local bar, no liberty to mine bitcoin at home, to host a youtube channel etc). GP and me also have to submit to a complete inspection by some USCIS officer every 3 years - and any offense, real or imaginary, can bar us from returning to the US at any time, without trial or even an explanation.
[1] http://www.rnlawgroup.com/news/518-82-5-years-wait-time-for-...
This kind of discourse around immigration in some circles is extremely short-sighted. Every time America has taken in a wave of immigrants - whether unskilled or skilled (e.g. scientists fleeing Germany in WWII) it has been a net positive for the county in the long run. The idea that labor is a zero-sum game - where a job occupied by an immigrant is one not going to a native - is ridiculous on its face.
Consider a similar idea on the consumption side - "if an immigrant buys a TV it's bad because that means an American won't be able to get a TV" - to see how silly it is. But years of propaganda about "immigrants taking our jobs" has somehow turned this into a truism.
In conclusion, please read some research on the topic before trotting out this tired talking point [1][2][3].
[1] http://www.migrationobservatory.ox.ac.uk/resources/briefings...
[2] http://www.hamiltonproject.org/papers/what_immigration_means...
Two people are hardly ever equal when it comes to applying for a job, its not just about skills, its about the people, its about the experiences they have had. I would always employ a person with more life experience than not, and traveling, learning a new language, a new culture is apart of that. It takes bravery, courage and stamina to uproot your life and move to a new country and these are all respectable traits. So respectable in fact, that the fear of these people by society is blatantly evident.
You forget that we are all citizens of the world, and people move around for many different reasons. Just because you are happy to stay in your cultural bubble doesn't mean other people are. And if these people are skilled and can contribute to the economy, even better.
besides equal skills could be bringing a valuable experience (eg: Knows the <Country> market better than a national)
Another answer to your question is, so that Americans can get jobs in other countries.