antiimmigration policies.

One problem with anti-immigration, flat off-the-bat, is that it involves force and coercion.
Another problem is that it's based purely in national selfism, and I'll explain why.
Obviously, immigrants want to move here because they perceive it'll be a better place to live.  Now this implies, among other things, that we probably have an imbalance in wealth vis-a-vis the other nations; this is true.
Some people feel they don't 'deserve' the benefits because they weren't born here..how lucky are those ignorami to have been born here?
In any case, as long as there's the imbalance of wealth that makes people want to move in, allowing people to move in alleviates the imbalance.  Lemme explain.  Their allowance is analogous to if we were to slowly expand the country to include areas in other nations.. only we just assimilate their peoples instead.  Now, yes, you might say that if they don't work for it then they're just leaching.  The facts of the matter are a) just because they're foreign doesn't mean they'll leach, b) some natural citizens leach, c) working for anything doesn't help the Earth and that's a pretty big variable in any system, and d) they already belong to Mother Nature by virtue of having been born, and your laws and order have no say on what areas of land they may stand on.  If you don't believe in Mother Nature, I'll say it a different way: land has been there for billions of years, people have been here for millions, and governments haven't.

If the country gets overcrowded by immigrants, then it gets overcrowded by immigrants; that's the price to pay for being so better.  But, obviously like Adam Smith's invisible hand, if it gets so crowded that the imbalance of wealth is alleviated enough, and/or they just get tired of crowding in the streets, then they'd stop coming.  So basically they *can't* leach off the country more than it would take to balance the world anyway.

Now, in the particular case of the USA, we have a very large imbalance of wealth.., so protecting the country from immigrants is probably, to some degree, protecting the imbalance of wealth, per se, and that ain't noble either..because it's the imbalance, among other things, that's killin' the world.