Good on you for listing your gripes with them. Too often I see people complaining about PayPal in general but I've managed to miss actual reasons before now.
Things like getting your funds frozen by Paypal when you're a legitimate business and handed over a fuckton of documentation and proof of legitimate orders to prove it. Which then destroys your cashflow, which means the typical 'pay in 30 days' that is extremely common in business 2 business transactions gets messed up because Paypal froze your money. You can't pay your supplier, your order doesn't come in, meanwhile you've been shipping your product to your customers despite the fact all the revenue from these orders is getting insta-frozen, and now you're starting to actually get legitimate issues of customers not getting their product because you can't pay your supplier for new product and can't ship to your customers, which makes Paypal clamp down ever harder to 'resolve these issues before we unfreeze the account', which of course is an issue they created and an issue that can't be solved because they're kidnapping your money.
So now you need to find external financing (we're not talking about Amazon here, but commonly 1 or 2 people selling products from their home, the internet's mom & pop stores) to fund the supplier's order, then ship, cancel customer's orders so you can prove to Paypal you can ship to every placed order (who leave negative feedback, understandably), and see customers cancel orders themselves (more negative feedback), and then unfreeze the money, pay back your financier, place another order with a supplier and hope to regain lost customers.
And that's the simple story, the true story is extremely frustrating and much more complex with cashflow being frozen for 6 months while you're trying to keep your business alive. Not everyone wants to recount it every time they want to criticise Paypal.
Now if there were legitimate concerns, cool. But as nailer said, you can find tons of stories of people who ran into these issues for no reason and without a reason given, without due dilligence and without the type of 'reasonably swift' (i.e. days or at most weeks, not 6 months) recourse & resolution of frozen cashflow you need to run a business without going bankrupt.
A tip, if anyone ever does a product launch with Paypal, call them beforehand. Launching a product and selling in a spike the first days/weeks (i.e. extremely typical for virtually every launch ever) is a red flag for Paypal.
Which means for anyone doing a pre-order, well you're fucked if you get unlucky. Plenty of stories of people doing a legitimate pre-order campaign with customers willing to wait say 2 months on the product. Halfway through your pre-order campaign you think 'alright I'm at $60k right now, I'll probably make it to $100k. I'll start to order from my supplier about $80k's worth for now to be on the safe side. You pay $25k of your own money upfront'. Campaign is over, you reached $100k, your supplier is busy, you call him up to adjust to $100k, and tell him you'll pay the remaining $75k right away. Turns out all your money is frozen. Supplier won't ship, Paypal won't unfreeze the money for months. You inform your customers, they're sad. 3% of them files a complaint with Paypal for a refund, which now means that 100% of Paypal's feedback from customers about you is negative, seeing as you haven't been able to ship to anyone yet.
You might think well good, Paypal protects its users from fraud (despite a total ignorance as to how normal pre-orders work, thereby screwing over their users), but this stuff happens to people who've done business with Paypal for 5-10 years. It happens to companies with solid internet reputations that takes 5 seconds to review on the internet or with a phonecall whether they're legitimate.
And that's the 'normal' stuff, i.e. selling a videogame, a bracelet, a usb charger etc... But if we get to the really controversial stuff, like omg sex on video, I know I should use the p-word but I'll just say it, porn... did that get censored? Well then you're out of luck with Paypal entirely, which is insane.
Also worth noting that their terms are pretty seller- and user-hostile. You described some of the seller-hostile instances above (here's another [0] from a few years back).
But they've also rolled out some pretty user-hostile stuff in the past year. At one point, they were set to roll out a new privacy agreement that included permission for them to robo-call you at phone numbers that you hadn't provided to them (with no mention of how those numbers were obtained).[1]
Also they're happy to support hate groups, but blacklisted wikileaks.