(or "The Sacrificial Character")
The somewhat contradictorily-named "Essential Ant-Man", our topic for this week, is almost as interesting for what you won't find as well as what you will find. What you will find is an interesting little early Silver Age collection, with a storytelling engine that's still trying to find its way from the horror anthology it once was--in the initial story, Henry Pym is a typical horror-story scientist, creating his shrinking serum, freaking out at its effects, and destroying it "once and for all". Later, as the series becomes more super-hero oriented, they still include the occasional one-off tale, pitching it as a story the Wasp tells to sick kids at a local hospital.
What you won't find is the element that's come to dominate Henry Pym's character over the last several decades, whether it be in the form of Ant-Man, Giant-Man, Goliath, or Yellowjacket; namely, his mental instability which has manifested itself in domestic violence. (In the "classic" Marvel Universe, this has been confined to a single incident, but Ultimate Hank Pym is a more habitual abuser.) There's not a hint of this in the low-key, slightly goofy romance between the bookish Pym and the flirty Janet van Dyne shown in 'Tales to Astonish' (and, via the magic of reprinting, in the Essential Ant-Man.) So where did this element of the character come from, and why wasn't it there from the beginning?
One obvious answer is simply that the "maturation" of comics--the desire to tell stories skewed to an older reader, with more ambiguity in its moral development--produced an atmosphere in which it was possible to talk about spousal abuse. Pym was allowed to become a less sympathetic character, according to this theory, because writers were willing to be more honest about their protagonists.
But this doesn't explain everything. After all, Ant-Man isn't the only character who "grew up", but we don't see an honest exploration of Batman as a child endangerer. When Spider-Man hit Mary Jane (during the "Clone Saga"), it wasn't the taking-off point for decades of discussion of Spider-Man as wife-beater. What separates Hank Pym from other super-heroes is very simple: He didn't have his own series by then.
It genuinely is that simple. The demands for a protagonist in a solo series are very different from those of one of many protagonists in a team series. The dynamics of an ensemble cast makes any given character more...well, more disposable, to put it bluntly, and while the team of Ant-Man and the Wasp requires you to want to keep reading about Ant-Man and caring about him, the Avengers can and did continue without Henry Pym. In fact, Henry Pym as unstable personality becomes a much more important element of the storytelling engine of the Avengers than he ever was as a boringly sane super-hero. The question of "Can he be trusted?" provides a lot of storytelling options, while his previous role (as just another of the many science experts on the team) could be filled by any one of a dozen other super-heroes.
Ultimately, in order to serve the larger interests of Avengers fans, Henry Pym was forced into an antagonistic role. Ant-Man fans might have been upset, but importantly for our purposes, there simply weren't enough of them to count.