I think there are a whole bunch of factors, including (randomly): 1) The disconnect between the value some people place on pets/animals versus the other (so there's no real uniform societal value). This exists within some families, too, so it really sets up conflict (how often have you seen one of the owners be like "let's just euthanize" and the other is all "do anything!"). 2) People don't actually pay much out of pocket for <most> of their own health care. Yeah, there are plenty of exceptions, so all of you that have high deductibles can simmer down - but generally, the costs are frequently 'hidden' from people. 3) A bit of internal guilt - they didn't set aside money for Fluffy's FB surgery, they don't have the cash handy, they feel guilty, so they take it out on us. 4) Genuine sticker shock - they don't <expect> the FB surgery to cost $1k-$4k, so of course they're shocked. 5) The 'car mechanic' problem: I have no clue if/when I'm being totally ripped off by my car mechanic because I don't know jack about cars. He could tell me my car's warp core needs replacing and I'd be like "Ok, sure, dude, how much will that cost? And when did they start putting those in, anyway?" People feel some of that with vet med - they don't understand it, so they don't know how to assess what's necessary, reasonable, appropriate, etc. They feel like they could be taken advantage of, so they worry they ARE being taken advantage of.
Combine all those and yeah, they'll say stupid things.
I don't really blame most people when they pull this stuff out. It is what it is and they're frustrated and so they react poorly. Occasionally when one really pushes .... I had one guy that went over the line and got aggressive about it, and I flat out asked him if he would give my kids free piano lessons (he was a music teacher) because he must care about teaching music, right? (No, it didn't go over well. No, I didn't expect it to go over well. I was kinda beyond caring and I let it get to me.) People like the Fenton article are, in my opinion, "over the line" .... because he's gone from exam-room frustration that is understandable to taking it out on vets in the public media when he had allllll the chance in the world to go get more information and present a balanced opinion.