The Great Purge was real, but not how the west claims. At that time, the USSR was under threats from all sides. Nazi and polish intelligence had infiltrated the highest ranks of the soviet state. Same with reactionary groups, such as anticommunists, mensheviks and trotskists, who often collaborated with nazi and polish intelligence. First Sergei Kirov was murdered, which launched The Moscow Trials, which uncovered a vast network of spies and trotskists trying to destabilize the USSR. Seeing this, Stalin ordered NKVD head Nikolai Yezhov to begin purges to root out all these enemy elements. Keep in mind that the USSR was preparing for the eventual war with Nazi Germany. The problem was that Yezhov himself was a nazi and polish agent. He decided to begin mass purges, forced confessions and extrajudicial executions against innocent people in order to create popular anger against Stalin and destabilize the soviet government. This went on for about a year, until Stalin found out about this, removed Yezhov as head of the NKVD and appointed Lavrenti Beria, who prosecuted all those involved with this including Yezhov and stopped the purges. So yes many innocents were killed during The Great Purges but not on Stalins orders. Also many guilty people were killed to protect the USSR and socialism.
To learn more on this i recommend Grover Furr's books, he debunks many of the "stalinist crimes". "Yezhov vs Stalin" by Grover Furr is specifically about the great purges. Then you also have "Blood Lies" and "Khrushchev Lied" also by Grover Furr, which debunk more general antistalin myths, including also the great purges but in less detail. You can download all of Grover Furrs books, including the 3 i mentioned, in ebook (epub) format for free here:
https://it.es1lib.org/book/12078299/732fa9
This was something I asked about before crossing over into becoming an ML too.
Let's say for the sake of the argument that Black Lives Matter launched a revolt against the US government and managed to overthrow it. Christian Nationalist Trump supporters wouldn't just all spontaneously disappear the moment the US federal government itself collapses. Mostly likely they would organize into underground militias and engage in terrorism and whatever subversion they could against the new government BLM would try to establish. Do you do nothing when those people like that are going around bombing and shooting people and attempting to regain power or do you utilize the state the stop them with so called "purges"?
In the Soviet Union it's also worth noting that there was also some people cases with people such as Nikolai Yezhov who were people with hidden right wing agendas inside the NKVD that carried out excess purges with the intent of facilitating anger against the Soviet government.
So the short answer is that yes the Great Purge did happen, but most purged were outlaw remnants and underground cells left over from the Russian civil war as opposed to just random people on the street caught saying nasty things about Stalin like propaganda implies. The number killed is also greatly exaggerated by propaganda, closer to around 600,000 rather then the 40-60 million that comes from the Black Book of Communism.
hundreds of thousands is still a lot, and mass executions/murder are surely not healthy for a country, even if those are people with dangerous beliefs. imprisonment or reeducation would be more humane. i would also hope that they were given fair trials before their punishments.
You're right, it's not healthy for a country, but considering the USSR was under the threat of (and eventually actual) war, and influenced by espionage and sabotage, it's at least understandable the party had this period of repression. Besides, the people, the workers in general, were not affected at all by this, most of those who suffered from repression were high-ranking party members.