No, that's like us telling you that you're not allowed to oppose immigration to Britain, unless you happen to be a pure-blooded Celt. The US was a nation of immigrants 100 years ago, most people today are several generations removed from immigrant ancestors. And economic effect does not define the value of a law - environmental legislation is bad for the economy, slavery was great for the economy.
The real problem here is that there's a fundamental contradiction between the law and tradition - people who support strong enforcement of immigration laws are in favor of the principle of the rule of law, whereas traditionally the US has had porous borders. Immigration is a contentious issue, because we have a complicated, screwed-up history of immigration, and the related issues of civil rights and citizenship (no, not just for blacks, pretty much every group that is non Anglo-saxon has been discriminated against at some point) - should we give politically guaranteed rights to those who abuse that government? And then we have to talk about TAXES, and any issue that involves taxes immediately turns into a giant clusterfuck.
The solution we really need is something like this:
1. If you get caught hiring illegal immigrants, you lose your license to do business, or get fined up the wazoo. Anyone who contracts with a company that hires illegal immigrants should also be fined for contempt of immigration law.
-My personal anecdote here, I work for a large corporate chain of supermarkets, and our stores contract with third-party companies to have people come in and do the cleaning tasks. Those people who come in to pick up trash and clean floors are of dubious legality, but since they're not hired by OUR company, they don't get benefits, and the corporation gets away with questionable labor while protecting itself from legal action. It makes perfect business sense, but it's fucking disgusting.
2. Widespread availability of a legal workers permit program. Anyone working without citizen or a workers permit would be subject to all penalties up to deportation - and this won't happen because it's just as bad for the economy as ejecting all the illegal workers, if you have to pay them minimum wage, there's no benefit to hiring them, so it's contrary to the business interests of the country.