Such a person would be an asset and if there were an infinite supply of jobs to employ such people in, we wouldn't need to restrict immigration nearly as much.

Such a person would be an asset and if there were an infinite supply of jobs to employ such people in, we wouldn't need to restrict immigration nearly as much. Every new skilled person we get would contribute to and grow our economy. However we don't have an infinite supply of jobs and every job taken by a skilled person from another country could have been taken by a skilled person from within our own country, had they developed the skill. It also reduces demand for those jobs, which reduces the motivation for people within the country to train themselves to perform it in the future and increases our dependence on immigration. My argument isn't that immigration is bad, I'm an immigrant myself (Australia -> US) but it's definitely a trade off and needs to be controlled carefully.