The vast majority of us seem to be guarded or private about it in most situations, with the notable exceptions being forums, arranged meetup-ups with ABDL or ABDL-aware friends, etc.--situations where we don't expect to be judged. That's easy enough to understand. Outside of these situations, there are plenty of others where we (rightly) conclude that ABDL would either be inappropriate or would be misunderstood in a counterproductive way. For example, going to work in Baby Mode isn't a reality for most of us, and it's not difficult to come up with reasons why discussing ABDL with coworkers--especially if it's a fetish kind of thing--is risky and potentially harmful to one's career. But just generally speaking, the Wider World is full of situations and places where being or appearing to be something other than a whole adult just isn't workable. A very few ABDLs seem to enjoy waging war on those things. I'll tempt a few flames by declaring that, by my own observations, those are usually the people with almost nothing to lose--which I don't mean in a bad way...exactly. But therein lies a big part of the disconnect between the small group of people who view ABDL acceptance as a "cause" and those who don't.
I know that's bound to have offended somebody, so I apologize in advance.
So, basically, we're spread around a bit, but I'll wager most are in the "private" corner.
I consider my DL-ness to be a private thing. It's a fetish. When considering whether I discuss ABDL with somebody, I sort of have to consider: Would it be appropriate for me to discuss any other aspect of my sexuality with this person? In this situation? The answer is almost always "no". Unlike a gay man whose sexuality probably comes paired with a reasonable desire to express affection for his male partner while in public, the diaper aspect of my own sexuality misses nothing by staying in my pants. Truly, nobody needs to know, nor would their knowing help me at all. So privacy is cool with me!