So let's start with the nuclear thing.
Russia is a bad actor. It treats its own people poorly, doesn't have a free press, doesn't allow free speech, it blocks a bunch of the internet so it's harder for people to find the truth. You get thrown in prison because they don't like you. Under the Soviet Union they killed millions of their own people in stupid famines from poor authoritarian decision making. They throw you at the meat grinder of the front lines of poor wars and destroy everything, because they do not value human life. They got nukes to make their bad behavior invulnerable. Ok, so fine, the world is a little worse off, but that's Russia.
Russia spread communism to Korea, since they have had a long-term strategic interest in Korea as a basing for attacking Japan in order to control more warm water ports. Japan and Russia have had conflict around this since the 1800s. It's not new. So Korean war. Now North Korea has nukes. They make their people suffer. The world is a little worse off, but that's North Korea.
Russia spread communism to China for many reasons too. China killed countless millions of people through poor authoritarian decision making too, through yet more famines. They kill any of their own people who don't agree. They took over Tibet by force. They execute more of their own people than the entire world executes, combined. They started building up the largest military mankind has ever seen and now they have nukes. Now that they feel invulnerable, they engage in the largest influence and interference campaign in world history, manipulating countries at scale and spreading extreme propaganda worldwide. It is all pervasive in social media comments, YouTube and elsewhere. I've seen this shift happen personally, slowly. It is not organic. So fine, the world is a little worse off. That's China.
Russia tried to spread communism to Iran and helped the Islamic radicals overthrow the government, thinking the communists could have some control afterwards or exist as an alternative party. Instead the Islamic revolutionaries kill thousands of communists to say, "no, go away." Now we have an Iran that is explicitly friendly with Russia, China, North Korea and Venezuela, learning from North Korea's nuclear program, sending its scientists there. It engages in Islamic revolution in a way similar to how the Soviet Union was trying to spread communism before World War 2, with armed activist militant communist groups. They infiltrated Yemen and that caused the war there. They infiltrated Gaza and Lebanon and Iraq. Afghanistan HATES Iran, because of their attempts to infiltrate it with their radicals. Iraq went to war with Iran, because Iran was engaging in revolution inside their country. Now Iran had built up a huge conventional military just like its friends Russia, China and North Korea, and aims to get a nuclear weapon to make their bad behavior invulnerable.
Iran can't be compared the same way as other countries that have nuclear programs, because most countries aren't Russia, China and North Korea which Iran is patterning itself after and buys military hardware from.
We're done with "so fine, the world is a little worse off". This is domino theory. This is salami tactics, slicing little bits of the world one at a time until the steamroll is so strong it has passed the tipping point and physics no longer offers a way for you to push back the tide.
That is only 1 reason for attacking Iran and it is highly abbreviated. There are dozens of other reasons for attacking Iran, defending Ukraine and deterring China from attacking Taiwan. Dozens of other reasons for capturing Maduro and trying to reform Cuba.
The US doesn't want to have to do any of this. We'd rather just be left alone and leave others alone, but that is not the world we live in. There are people that seek global domination and they are not the ones that want you to have freedom of speech or value your life.