I don’t remember anyone opposing it, except for the Puerto Ricans themselves. They voted it down many times.
Puerto Ricans vote against statehood every time it's proposed, and they do it for a reason not mentioned in this article, and that is: As a Common Wealth, Puerto Ricans don't pay U.S. Federal Income Tax and they can't vote in U.S. Presidential Elections.
The only reason Democrats in this country want statehood for Puerto Rico is they think they'll be able to capture another block of "low information" voters, but most Puerto Ricans are a little more savvy than the Democrat Party gives them credit for; they'd rather keep their money in their pockets than be able to vote for the likes of Obama, and I can't blame them.