What the Soviets did with Marxism is not much like what Marx wrote. And the dictators starting with a paranoid Stalin used the prohibition on religion as a way to prevent the hierarchy in Eastern Orthodoxy from being a political conflict. In fact Stalin reopened churches in 1942 when the Germans were winning the war. He did this because he knew it would help calm the masses. So was atheism really a core element? Not when churches remained standing and preists remained in their posts. Services were banned until Stalin needed them.
Yes, the approach was pragmatic both because doing this often wasn't popular at home, and was also causing PR problems abroad. They also collaborated with the Nazis and used Western capitalists to help build their industrial system as they realised you couldn't magically transform into a communist utopia overnight.
While Stalin did ease off the persecutions during WW2, by then he had already destroyed most of the Churches in the USSR and killed or imprisoned tens of thousands of clergy, and after WW2 the persecutions resumed.
That they "only" eradicated 100,000 clerics and closed over 98% of the churches and all monasteries is not really much of a counter to the idea that they wanted to destroy religious belief.
USSR anti-religious campaign (1928–1941) - Wikipedia
It didn't start with Stalin though, it started from the very beginning with Lenin. The party elites had trouble bringing the proles along with them of course, but the philosophical underpinnings were always there and are explicit. The end of god belief was necessary, by whatever means it would occur. Some felt it would die out naturally, others felt it needed a bit of a push.
The philosophy long predates the USSR:
Marxist–Leninist atheism - Wikipedia
The more moderate wing proposed creating a religion of humanity, but Lenin found this to be weak-willed pinko appeasement:
God-Building - Wikipedia
While it has nothing to do with generic atheism and more than jihadism has to do with generic theism, many folk will insist that, unlike theism, atheism cannot be a motivation for any oppressive action in any way even when combined with other beliefs. This is a nonsense though as no beliefs exist in a vacuum, and if you strongly believe there is no god
and you think belief in god is an impediment to a vastly better world, then of course this can lead to a desire to forcefully speed up the process.
If this view is utopian, combined with a staunch materialist view and the idea that morality is simply what humans make it you can create a very violent "ends justify the means" logic. Infinite upside alongside a view that an individual human life has no intrinsic value makes it possible to justify horrendous short term suffering for the 'greater good'.
As an atheist, I don't really understand why it is even so important for other atheists to try to deny atheism was a key part of Marxist-Leninist ideology. They were pretty explicit about their views, and as I'm not a Marxist-Leninist then I feel no greater need to defend their views than I do for Nazis, Jihadis, the KKK or any other group who I don't personally identify with.
Humans of all stripes can be good or oppressive for different reasons, and belief or disbelief in god can play a role in that, or it can play none at all. In the USSR, it played a role.