The issue is that groups of immigrants can form enclaves where they speak their own language but not the local language. This has the effect of making them “second class” and limiting both their economic opportunities and their overall contribution to society.

This implies that each of us is in charge of whether we are "second class" citizens or not. It's the people in power who control the social structure. They decide what "class" a person is. Immigrants are often attracted to their own communities not just for comfort and familiarity, but also for practical reasons. These communities step in where the government fails to. They help new arrivals find jobs, transport, and places to sleep/live. They enable people to have their basic needs met, in a country run by people who already think that poor immigrants aren't the same class/worthiness as they are.

It doesn't have to be this way. If the people in power gave a shit about the rest of us, if they truly wanted immigrants to thrive, they would build a social structure that actually enables that. Immigrant groups don't inherently limit their own economic opportunities - those limits are created by those who treat them as "less".

One last thing - to say that immigrants' "overall contribution to society" is "limited" by them being in their own communities, implies that any of the work done within those communities doesn't count as "contributing to society." It also implies that the jobs that are usually filled by immigrants, such as crop-picking and other agricultural work, are jobs that don't contribute enough to society. Yet I'd argue such people contribute more than many U.S.-born people I've met.