Edit: I'm deleting my response and reposting Rick's:
(1) PA is the number of times a batter goes to the plate with a chance to get a hit.
(2) H/PA is the percentage of times a batter gets a hit out of all his chances to do so.
(3) AB is a different number, not representing all of a batter's chances to get a hit.
(4) H/AB is a measurement that everybody's historically familiar with, and it measures a very specific thing. But that thing is not "what percentage of times does a batter get a hit out of all his opportunities to do so."
(5) H/PA does not "penalize" walks as a "negative" outcome, as you assert. It merely categorizes them (accurately) as "not a hit."
(5b) Just because H/PA will always be lower than H/AB does not make the owner of said stat "worse." THERE IS NO PENALTY. You compare H/PA vs. H/PA; you have no earthly reason to compare H/PA vs H/AB in terms of determining a player's skill.
(6) Rate stats will be more useful and descriptive if they all started with the same denominator. At some point in ancient history, AB was invented and put into use. But pragmatically speaking, PA covers the entire universe of batter opportunities, and if you're going to go with the Single Denominator, it's the only choice. Classifying BB and SAC as a "non-hit positive outcome" is good and right. Putting them entirely into their own universe -- different from hits and outs -- is not.
(7) And that's why I'd be happy to endorse any move to H/PA and BB/PA replacing H/AB and H+BB/PA: AVG is inherently built into OBP, and you can't do anything useful with the two numbers, since they have different denominators (but I guess that doesn't stop people, since OPS is A Thing, even if it is a thing that is the sum of two numbers that are measured on two different scales). Meantime, H/PA tells you what percentage of times a guy gets a hit, BB/PA tells you what percentage of times a guy gets a walk. And as a bonus, you can add the two numbers together (and magically get OBP as a byproduct), because you're using the same denominator. All rate stats for all batting outcomes can then be directly compared and related.
Near as I can tell, the only real reason to be attached to H/AB is the simple familiarty factor. We know what AVG means, and maybe you don't want to go learning another scale where .260 makes you a All Star. I can dig that; part of me even feels the same way. But that's no excuse to not grasp the basic concept at play here...