“Superman” hasn’t even opened — and it’s taking a beating in conservative media over possible pro-immigration messages due to comments from the director … and one former Superman says that super-sized mistake might hurt the box office.

Here’s the deal … James Gunn told The Sunday Times the movie is about an “immigrant” and “basic human kindness” — a value he says we’ve lost as a country. Those remarks were pounced on by conservatives as a clear indicator the flick will be “woke” and preachy amid ICE raids via the Trump administration’s relentless deportation efforts.

Dean Cain, who wore the red cape in “Lois & Clark: The New Adventures of Superman,” tells TMZ … he was so excited for the new movie … until Gunn had to break out the political Kryptonite — and sour a portion of the fandom.

The outspoken conservative actor and occasional political commentor is pretty sure the immigrant remark controversy is enough to ding the box office returns … but he still hopes the movie is a success. Of course, Fox News’ personalities railing against the film won’t help … such as Kellyanne Conway saying, “We don’t go to the movie theater to be lectured to” and Jesse Watters joking that “MS-13” is written on Superman’s cape.

DC tells us is so frustrating as the comments from Gunn weren’t even necessary … ’cause we KNOW Superman is an immigrant — he’s a freaking alien! What’s more, Superman was created in 1938 just prior to WWII breaking out … and “Truth, Justice and the American Way” were — and still should be — crystal clear values.