Skepticism of immigration and diversity

I know this is an unpopular topic, but I see that throughout history that diversity -- of any form: religious, ethnic, cultural, racial -- has failed wherever it has been tried because it offers people a choice between having no culture or being ostracized for maintaining a cultural identity.

Immigration seems to be popular with the construction industry, cheap labor employers, and serf-masters like the big Silicon Valley companies. Cheap lawn mowing and cheap software production are high on their agendas. However, it's not really working in that this country continues to have clashes between value systems, including those rooted in culture, and increasingly, between our lack of values and anyone who does have cultural values.

Can anyone name a time and place in which diversity has thrived? It seems like all of our accounts come from a couple centuries later when the experiment has failed, and left behind a culturally-confused third world nation.

Perhaps instead of just walking lock-step with the rest of the herd, we should think independently about this issue, and unlike the rest of our society, question whether it's a good thing at all.