1) Selection of which contacts to message was opt-in. The OP decided that he wanted to send a message to a particular subset of his contacts.
2) There was a View/Edit message link that the OP didn't bother to utilize.
So between 1) and 2), we have case where somebody opted-in to having a service message their contacts, didn't look to see what that message was going to be even though they had the option to, and then got angry when they discovered they didn't like the content of the message that they could have viewed or edited beforehand.
The "I highly recommend applying... you'll thank me later" piece of the message is certainly inappropriate because this was a "get friend to vouch for you" feature, not a "recommend founder dating feature". Still, I don't see this as "spamming your LinkedIn contacts" nor a massive violation of trust. Also, OP's failure to mention the existence of the View/Edit Message link in his rant seems rather dishonest.
Edit: I'd love if the early down-voters could explain why they disagree. You seem to have read my entire message in about 20 seconds..
I am the OP.
(Of course, there is still the questionable practice of writing such an enthusiastic endorsement in the first person, but again you had final veto powers on the wording and you opted in to it. Such practices are unfortunately "par for the course" nowadays.)
This is the most extreme faux-1st-person endorsement I've ever seen. It makes schoolFeed look positively reserved.
Even if it were the norm (which, based on the response here, it clearly isn't), something being common doesn't make it the least bit right. That's the worst kind of complacency.