I can take these.
1. You are completely right, undocumented immigrants have no power to change laws in the US.
However, US citizens do have the power to change laws, and many US citizens want more rational and humane immigration laws. For example, a majority of US citizens want a pathway to citizenship for people here illegally now.
The reason we don't have immigration reform is because a minority of Tea Party Republicans are blocking the vote. They won't even allow a vote for such a law, because if they did they know that a majority would vote for it.
2. You completely misunderstand how the economy works. Economies run on people.
People work, they make money, they produce things, they start businesses, they buy things. People don't "suck economies" dry. Think it it this way, you aren't sucking the economy dry, and neither are I or my kids.