A Republican state senator thinks figured out why Illinois' economy is suffering: The state's LGBT-rights laws.

Sen. Bob Onder (R-Lake St. Louis) proposed a constitutional amendment that would allow businesses to refuse to serve same-sex couples, and says the Prairie State should have done the same.

“We look at states that have a lot of aggressive gay rights laws — Illinois comes to mind, Chicago — and they are some of our economic basket cases," he told reporters on Tuesday. "I really think that these businesses should leave well enough alone and let Missouri voters decide whether to protect religious freedom."

We're not sure how accurate his assessment is, as inclusive legislation generally leads to an economic windfall: In 2012, three years before the Supreme Court made marriage equality the law of the land, Mayor Bloomberg reported that same-sex weddings added an additional $259 million to the New York City economy.

If passed, Onder's amendment, Senate Joint Resolution 39, could could cost the city more than $50 million a year in lost business, according to The Kansas City Star.

But he insists the amendment would be a boon to the state economy: "If we look at states that have religious freedom (laws) — states like Texas, Utah, Oklahoma, Nebraska — we see some of our states that are growing the fastest," he said.

“I believe it is good business to support religious liberty," Onder said. “Defending religious freedom is not bad for business. In fact, it is quite good for business."

Democrats aren't buying it.

“If elected officials from Missouri want to welcome businesses to come to their state and discriminate against its residents, that’s their prerogative. But it’s not who we are in Illinois,” said state Sen. Heather Steans, who sponsored Illinois' marriage equality bill.

Steans (above center, holding plaque) also pointed out that Missouri's income tax rate is significantly higher than Illinois.

"If Illinois’ tax rates were as high as Missouri’s, we wouldn’t be struggling with the budget problems we have today," she said in a statement Wednesday.

Democrats in the Missouri Senate staged an epic 39-hour filibuster to block the measure, but Republicans forced a vote on the bill, which now goes to the House for debate.