I like the way A.E. Wilder-Smith explained this uniqueness.
God makes plain to all men his existence through that which is made. When men respond with either "I refuse to see it," or "I see it, but I don't care," they trigger the "giving over" Paul speaks of.
In short, Atheism, and more importantly, "functional" Atheism are the triggers to this judgement.
While there are few actual Atheists in this country, the number of Functional Atheists is overwhelming.
That’s good but I would key in on the meaning of those “who suppress the truth in unrighteousness” — which I take to be a further category beyond one’s personal unbelief.
This is active SUPPRESSION in all UNRIGHTEOUSNESS — and that gets God’s judgement upon that person with the most DEBASING and DISGUSTING THING a human being can ever be involved in (at least that’s the way God views it).