I think the most obvious importance of this issue is the fact that the current system of immigration and border security in the United States is broken. There is little incentive for people to come here legally since the process is so expensive and time consuming, while most people who come here are doing so because they are economically desperate.
While it is certainly true that the labor force immigrants (both legal and illegal) provide is currently necessary for our economy to expand and function, we cannot continue to both employ them and call for their expulsion and denial of services. We either have to revamp our economy so that immigrant labor is not needed and the prevailing wage will attract citizen workers (quite unlikely), or we need immigration reform to create a functional system that allows these workers to come here, find a path to citizenship, and become an open and valued part of the American workforce.
So are you asking why it is important to talk about this issue?
I think that it is important to talk about it for a lot of reasons. People with different opinions about illegal immigration will have different thoughts about why it is important to talk about.
If you think the immigration is bad, it is important to talk about it because it is having a bad effect on our country. It makes us disrespect the law because we see so many people coming here illegally without anything happening to them. It hurts our economy because we have to pay for the services that these illegal immigrants need. Finally, it makes it so that we cannot control our population.
If you believe that the illegal immigration is not such a bad thing, it is important to talk about it because immigration is a basic value of our country. We are supposed to welcome immigrants and we are not supposed to hate people just because they do not speak our language well or because they are a different color. We are supposed to value immigration also because immigrants are highly motivated people who will work hard to become productive members of our society.