Miller's play isn't directly about Communists, but witches were the Communists of the 17th century. This isn't to say Communists were laying the evil eye on anybody, but it's the same sort of thing: a permeating terror of an unseen foe who infiltrates every corner of life for some nefarious purpose.
The Crucible is an allegory, a story where one thing is used to represent another thing in order to, you know, make a point. Arthur Miller wrote The Crucible in 1953, which was the darkest year of the McCarthy Era. Now we know that McCarthy was about to get the smackdown, but Miller couldn't have known that.
In this play, Miller uses the literal witch hunt in colonial Salem, Massachusetts as a stand-in for the figurative witch hunt for Communists presently claiming the lives and careers of his friends. Even writing this play was an act of courage; Miller could very easily have been painted with the same fear-mongering brush and been humiliated and ostracized.
Instead, he got a Tony.
He got Marilyn Monroe, too, but that's another story.
McCarthy's most powerful and visible foe when the senator was at the height of his power and hysteria, Murrow was a seriously brave guy. While careers were going down in flames all around him, Murrow saw a man who was undermining the free society he was allegedly defending and decided he needed a punch in the mouth. He took on McCarthy at risk of being taken off the air as a Communist sympathizer, like many other broadcast journalists.
Murrow was a TV journalist. Back in the 1950s, that actually meant something, and Murrow took his responsibility seriously. Murrow's favorite tactic was to debate McCarthy or have McCarthy debate himself, which is a bit The Daily Show borrowed many years later using present-day politicians.
In this specific example, McCarthy had come after Murrow with the usual: unsubstantiated accusations. Murrow decided to do what his platform allowed: respond. In reasonable tones (and smoking the whole time, because this was 1954 and everyone was legally required to have a cigarette threading smoke into the air at all times) he refuted every one of McCarthy's allegations.
Murrow embodied everything McCarthy was not. Murrow was calm, reasonable, rational. Murrow responded to allegations with concrete, provable facts. Murrow never once stooped to insults or mud-slinging. Any allegations he made were backed up with fact.
We should all be like Edward R. Murrow.
Except the 3-packs-a-day smoking habit. Seriously, that's really bad for you.
In 1952, film director Elia Kazan appeared before HUAC and sold out eight of his friends.
On the Waterfront, a grimy film noir starring a young Marlon Brando going up against mafia-controlled union bosses, became Kazan's defense of himself. It's an interesting companion piece to The Crucible, as not only are they from the same time period, but Miller was a former friend of Kazan who became one of his most vocal critics. Kazan thought the leadership of the Screen Actors' Guild were a bunch of left-leaning pinkos. Like Brando's Terry Malloy, Kazan thought of himself as an ethical guy speaking up despite pressure from his corrupt superiors.
What could an admittedly awesome B-movie about alien shapeshifters taking over a small American town have to do with McCarthyism? A whole lot, but on an allegorical level.
The most successful horror movies reflect the fears and anxieties of the day. That's how they make money: by scaring people. The easiest way to scare people is to show them what they're already scared of. Invasion of the Body Snatchers played into fears of a vast and coordinated army of agents from a distant power who looked just like us but wanted to turn us into soulless monsters like Communists.