There are lots of "right" ways to parent. It's pretty much comes down to whatever works for you and yours,
until..... your choices infringe on the rights of others.
FWIW - I have 5 children, oldest and youngest are 20 years apart. As a young mother, (had my first at 21) I told myself... I won't make that mistake again! And ya know what... I didn't. I learned and never made the same mistake twice... I just made
different mistakes with each child!
I'm not posting on this thread to tell any mother, young or old, the way they handle their child's tantrums is wrong... handle it anyway you want, but what I am here to say is, if you allow your child's tantrum to become my problem, that is wrong.
This thread is more or less about what is or isn't acceptable behavior from children in public places, and the parent's reaction, or lack of, to the child's behavior. I really don't think there's much leeway to debate if allowing a child to scream through a show and ruining it for others is acceptable. There maybe explanations and excuses for the behavior, but I don't think most reasonable, mature adults would defend this as acceptable. Rude is rude. What could be argued to death is how a parent chooses to deal with the inappropriate behavior, but choosing to ignore it at the expense of the child or others is never the right choice.
I don't disagree with your last paragraph. And my post wasn't aimed at you.

I'm just confused how a random meltdown NOT in a show, etc. would become someone else's problem.

Most people that encounter a meltdown can walk away. I could see on an airplane, it would suck, yes. But a random meltdown in the parks?
There is a lot of judgement going on in this thread, especially of kids having average, ordinary meltdowns. I happen to agree meltdowns shouldn't be disrupting a show, etc. My kid would be outta there. Just meltdowns in general and how to properly handle them and what shoulda, coulda, woulda been done. Apparently all moms should have psychic ability to read when you kid is going to have the next meltdown, and be sure to leave the park so it doesn't disturb them.

Perhaps I'm reading it wrong, but that's how it's coming across.
I can't speak for others, but my kid is like Dr. Jeckyl/Ms. Hide. Sometimes just telling her she has to hold my hand causes an issue because she's little Miss Independent as well. You may happen to witness this in WDW. It's me.

Just sayin'. Do I have to run out of the park because someone doesn't want to see my kid freak out while I'm enforcing a rule?

I know my kids' meltdowns lasts about 5 minutes and then she goes on her merry way like nothing happened.
I expect to see all types of behaviors at WDW, just like I would at Chuck E Cheese, or another amusement park, or the Jersey shore. If we don't feel like dealing with kids, we go to Vegas.

I have sympathy for other moms, and would never, ever judge them based on a random meltdown we just witnessed.

That was my point. I happen to think teenagers are WORSE! And everyone that has teenagers tells me to ENJOY this stage my DD is in.
We are doing WDW for the first time as parents. Currently seeking advice on how to schedule breaks and when. But I 'get' it's the age, and just follow others advice the best way and apply it and hope it works. In the meantime I didn't know we should be worried if a random meltdown here and there disturbs other guests.

I kinda figured it's WDW and everyone should be paying attention to having fun and not how other guests are parenting their children.