In America or other nations there has to be an always shifting deal between different people and a race debate which is a debilitating factor, instead of focussing on more important issues every debate there is racialized. Something that would have been redundant in a homogenous so(y)ciety. People are divided by race, culture, class - and the less differences the more they have in common and the more effective they are in their actions.
The lie of liberalism is that people have common interests, this is not even true for people within one nation, often interests are mutually exclusive (like the ones of men/women) which leads to conflict, more differences will lead to more conflict. In Europe the UDSSR and the Königreich Österreich-Ungarn as well as Jugoslavia broke apart. "This doesn't mean that it will also fail in the future!" - it is simply not worth the risk when it never worked before.
Tolerance/equality/etc. are (if existent at all) only intermediary stages. True equality can never exist (at least not for long) - due to the Tocqueville effect the demands of a group will only rise the more they become satisfied, equality and egalitarianism are therefore inherent lies that will only satisfy people for a short amount of time, then the oppressed becomes the oppressor and this will repeat itself. With diversity the inner politics become the outer politics - and then it is not about deciding the fate of a commonly shared country, but rather about damage control between enemy power blocks.
Diversity is not a strength, but (if you look at the pictures of the racial riots and the burnt cities) the biggest weakness of the USA, why should you import that ticking time bomb into your own country? Imagine how these pictures were for every enemy of the USA, if you want the USA to be diminished greatly in its efficiency just orchestrate one single event that then gets picked up by the racialized media and then you don't have an exterior conflict anymore, but an interior one. America has become an empire which oppresses its own population while bringing its shitty culture under the disguise of freedom into the rest of the world.
Last but not least: Who wants it in our present days? Large corporations and (mostly misandrist and explicitely pro-feminist) cultural bolshevists. It's detrimental for everyone who isn't a landlord/corporatist/enjoyer of this modern, "free" world. Look at the Coca Cola memo - the workforce should become less "white" and "less white" is a synonym for better slaves, far more eager to work harder for less money, this migration enables loan dumping ad infinitum, rising rents (more people, same area, more demand, same supply), more competition among males for females (because most migrants are males), etc. Of course someone could say: "Well the system is to blame!" - yes, this is partially true, but this system is not changeable within realistic time frames and therefore your policies directly hurt us, an utopian future vision of leftism is something that nobody with an relevance believes in anymore, the current policies of financial redistribution don't affect any richfags, but rather the (white) middle class.