I'd argue it's not exactly fair to start a war without informing any allies & expecting them to jump in. I would argue that it wasn't the US that started a war. It was the Iranians who have been killing Americans for over 40 years. When the US finally says enough and fights back suddenly everyone has their panties in a bunch. European navies are not in a state to operate in the Gulf and provide any meaningful support. What they can do is power the U.S.'s global logistics network and enable it to project power globally. Did I miss something? Didn't Europe refuse over flight, airbase and ports to the US in Epic Fury and we were still able to pound Iran pretty good IMO. Without European bases & logistics, the U.S. will greatly lose its ability to influence nations as a superpower. Operation Epic Fury wouldn't have been possible without Ramstein AFB, or RAF Fairford, for example. Or without the massive airlift that went via Europe. I do believe the airlift was with American aircraft, not European, and it went to the Middle East not Europe.
It's the United States & Israel that Iran will nuke first if it does get a nuclear weapon. Look at North Korea, Kim talks specifically of nuking South Korea & the U.S., and has made ICBMs exactly for this purpose. I'd bet every bone in my body Iran will nuke the U.S. before it ever thinks of nuking Europe. I don't think Iran has the range to strike the homeland here yet. They do have the range to hit American bases in the Middle East and Europe
Regardless, this isn't about Europe - it's about the U.S.'s Gulf allies as well as Israel, who are the ones who took the brunt of Iranian attacks.