For starters, "Gulag" just means "prison." Of course prisons existed in the USSR, and some had rather brutal conditions. Others, however, did not, and treated prisoners better to much better than your average American prison. Nobody is saying the Gulags never existed, perhaps they mean your specific interpretation of the conditions of gulags and the extent to which they were used. Edit 1
As for Stalin himself, it's fair to say he committed a fair degree of errors in judgement, had reactionary social views such as his view of homosexuality, was frequently paranoid, and so forth. At the same time, it is equally fair to understand that Stalin has been the subject of countless lies, exaggerations, myths, and other degrees of Cold War propaganda we learn as fact despite evidence to the contrary, especially following the opening of the Soviet Archives. Moreover, it is necessary to acknowledge the vital role he played in governing the worlds first Socialist State, and building the foundations of this rapid improvement on the utter squalor of the Tsarist regime.
Should Stalin be idolized? I don't think so, as I believe that can get in the way of accurate analysis. Should Stalin be villianized and made a scapegoat to brush the Red Scare under the rug? I don't believe so, either. The USSR came with countless benefits, from a doubling of life expectancy to free healthcare to near 100% literacy rates (better than the modern US), and more. These benefits were formed under Stalin, and as such we must do our absolute best to separate fact from fiction. If we accept and push purely the accepted bourgeois narrative regarding the real experience of AES states, then we cannot learn from them properly and sort out what worked and what did not.
Basically, Stalin was neither a perfect saint devoid of mistakes nor a unique monster that should be especially condemned. He was the leader of the USSR, but did not have absolute control, and in addition was in many ways less monstrous than contemporary leaders such as Hitler and Churchill. Correct contextualization is important. I highly recommend the short, 8 minute article "Tankies" by Roderic Day, hosted over on Red Sails. For more in-depth reading, Stalin: History and Critique of a Black Legend by Domenico Losurdo is a good historical critique of Stalin that focuses on taking a critical stance towards Stalin and contextualizes him.
Edit 1: seeing your other two comments, I am now entirely certain that this is the case.