One of my favorite things an anime can do is offer up uniqueness. My favorite anime of all time present such interesting and unique mechanics, characters, worlds, or just enough bat-shit insanity that it's hilarious.
Death Note has more symbols for Christian theism than a praise band drummer (it sounds better if you say it) and is so grungy and serious in its concepts that it's a marvel that it can remember to have fun with itself at times.
Soul Eater is funny with an amazingly fleshed-out world and compelling characters with interesting quirks that always feels like shit has a purpose in either forwarding the plot or expanding the lore (even the Excalibur episodes, fool).
Nichijou is the aforementioned bat-shit insanity with an OP that makes me cry with joy and a direction of no direction and a focus on the lack of a story through-line aside from the coinciding groups of main characters.
And JoJo has a mix of all these with just enough bs happening in each and every episode/chapter for you to just accept the bs in following ones. A Stand that's a wall-socket? ...Sure.
But of course, you're here to see me say why Part-skippers should not be crucified.
But that's exactly why they shouldn't be. Uniqueness.
I know a couple of people who hate JoJo because they tried to get into it through Phantom Blood and Battle Tendency, and I know why:
They hate Shonen anime.
As weird as Parts 1 and 2 are, they are still more prototypical Shonen than Part 3 onwards. When Part 3 kicks in, not only does each battle become more focused on the enemy's powers and how to defeat them with the main character's own powers (something that was in Parts 1 and 2 but more of an undertone there), but it also becomes a different genre all together in each and every installment.
Like Mother's Basement stated in their special on why JoJo is so awesome, Part 3 is a globe-trotting odyssey, DiU is a more contained and light-hearted mystery with a darker central plot than it lets on, Part 5 a gang story all about the characters, Stone Ocean is a Jailbreak, SBR is a Western and Part 8 is a darker take on Part 4.
Want comedy? Diamond is Unbreakable will get you enough. How about more serious stuff? Parts 1-3 (or as I call them, the Dio saga) is pretty good fare for that while still providing enough levity.
The thing is that not everybody will like all the genres in JoJo. Not everyone will enjoy the Dracula story of Phantom Blood, or the more personality-driven Battle Tendency.
To be fair, I watched all of the Parts in order, but I started watching Part 1 and just couldn't finish it for months because I wasn't very interested in Jonathan, Zeppeli, or anyone else particularly in the whole Part. I finally finished it and immediately liked Battle Tendency more, due to Joseph taking things less seriously, the lack of Dio, and the building of the world that was still being introduced.
In skipping these parts because one isn't enjoying them, what is one really losing? Context? Yeah sure, I guess, but the wonderful thing about JoJo's Bizarre Adventure is that it's designed to join in with at any point. I feel like that was the probable cause of the alternate universe in Parts 7-8: to make those more accessible to new fans. Each part is constructed to build off the previous ones but also have enough of their own ideas to warrant looking into as whole separate anime.
Take for instance, Part 7, which was a new start for the series in an alternative universe around the same time that Jonathan was fighting Dio in the first continuity. It had Stands, yes, but it also had the Spin, a new mechanic for those jumping into the series for the first time to latch onto alongside fans who were looking for fresh ideas to read and Araki himself who was looking to write about something new.
Notice how few characters from previous Parts consistently show up. The most was found in DiU with Jotaro and Joseph, and Joseph only came in around halfway in. In Part 5, Jotaro and Koichi were there, but after Giorno joins Passione, they cease to appear at all. There's just enough to give returning fans a throughline so as to not really get in the way of a new fan's enjoyment. It all ties back into the bigger picture but at the end of the day each Part is about its own ideas.
If someone enjoys the Part that they watch or read, they'll most likely go back and watch/read the ones they skipped to learn more about the story. For instance, reading Part 6 will send someone back to the start to learn more about Stands and predominantly DIO, Pucci's obsession.
With such care taken by the immortal god known as Hirohiko Araki to make the series so accessible, I find it quite ironic for its fanbase, one of the most passionate and excellent out there, to be so hostile towards those who take advantage of that accessibility.
TL;DR: Don't hate on part-skippers when keeping those people in mind is a core value of Araki's writing. :P