I believe it's a classic business mistake to think that you must turn a profit on every single customer. It's much better to think like a casino: as long as you're in the black for a service and segment of customers, it's a win.
That's especially true for PayPal now. Before merchants didn't have much choice. If PayPal continues to be seen as difficult and risky, the better-qualified merchants will be the first to shift to other services. That will leave PayPal with a much more risky customer base than they have now.
I don't think any reasonable person has a problem with PayPal deciding to freeze funds in order to ensure that they make a profit. The problem is that, once they have done so, it requires Moses and ten Biblical plagues in order for them to let your money go.
I don't have a problem with PayPal putting a temporary hold (delay) on new funds coming into an account (as long as it's clear what the guidelines are for such a policy), but what I do have a problem with is PayPal freezing an entire account, including funds that are more than a year old. Which PayPal absolutely does in some circumstances.
5-year ex-paypal customer (and hated being one the whole time). 6-month stripe customer (and happy every minute of it so far)