PayPal is not a competitor to Facebook simply because they are pursuing different ends and serve different purposes. PayPal is a payment system and Facebook a social network, they are not competing with each other for their clients. The same individual can be a user of both PayPal and Facebook, using them according to his needs as required. Honestly, it is strange even to see such comparisons.

With altcoins, though, it is a completely different matter as they are all competing for the same money of the same people. if an individual invests in one coin some amount of money, he can't already invest that money again in another coin until and unless he disinvests it first. This is the essence of and reason for competition between altcoins, which is simply not possible between PayPal and Facebook. There's simply nothing for them to quarrel over, unlike altcoins.