I've been thinking about your post for a few days...
I decided that the answer is, "If you have to build a case for it, something is wrong."
I've seen lots of analysis of "when to buy" over the years... (all the "pundits" say 100 hours a year flying, minimum... which I translate into "two hours EVERY weekend, or longer flights that mean you don't fly EVERY weekend")... but the end game of that decision is really this: Do you want airplane keys in your pocket so you can go fly whenever the heck you feel like it? Because that's the REAL reason to own... other than being mildly annoyed by your own airplane when it's grounded for maintenance.
And I've seen lots of reasons to go flying in "mission" format... the $100 (nowadays, $200) Hamburger Run, trips, just messing around in the pattern, sightseeing, etc... and I've come to figure out at all of those exist or don't in rentals OR owned aircraft... so unless you have a need to be gone for long periods of time with the airplane (since most places will either charge a minimum number of daily hours or similar, and will start squawking if you're gone with their airplane for two or three weeks...) or a need to equip the aircraft in some special way that only you like (maybe you're a hard-IFR traveller and want solid backup systems and the very best IFR tools)... none of them seems to REALLY apply to the "own or don't own" question.
So now you're down to... "Become a pilot, or not?" ... and that one... just falls to "Who do I want to be?" after you try to figure out all of the above... the only time I would really caution someone NOT to become a pilot is if they absolutely KNOW they don't have, or won't make time to stay reasonably proficient... in that case... you're raising risk to yourself and passengers.
Clear as mud, eh? Just sayin'... in the end, it's just "Who do I want to be, and what do I want to do?"
Having been an owner now for a while, I'll fight pretty hard to STAY an owner... I love the flexibility of "keys in my pocket", even with an occasional blip in the schedule because my co-owner is flying... it bugs me a whole lot less knowing it's not someone "anonymous" on a rental schedule that I'm waiting on... it's someone who cares about the airplane as much as I do.
And having been a pilot for much longer... I just want to be a pilot. I can't really justify it financially at all. In fact, fiscally it's stupid. It's just what I want to do/be.