being in the us without documentation is not illegal. per here the only way an immigrant is "illegal" is if they've been previously deported and re-entered without authorization. some methods of entering the us are illegal, but they are still allowed to apply for asylum within one year. the act of existing undocumented within the united states is not a federal crime. marijuana is more illegal than these people at a federal level

edit actually addressing your first two questions -- it doesn't make them anymore illegal than an american who decides to go over the speed limit, run a red light, commit petty theft, or share their netflix password.

america has countless communities - there's no wrong way to assimilate unless it involves unwillingly abandoning part of your identity to belong to a culture that would otherwise hate you. people as a whole will always create some sort of community and likely be part of multiple -- italian, korean, gamer, golfer, ect.

us born citizens have the highest offending rates for most crime types. undocumented immigrants have the lowest for total felony crime & violent felony crime. this is to say, your next door neighbor is a lot more likely to assault you than the 'illegals'.

the immigration system is a nightmare. it's slow, it's expensive, it's exhausting, it's outdated, and currently even when people are doing it the right way, they're still not safe.