Last month, the Writers' Guild held a survey asking its members if they believed in writer's block (the possessive apostrophe donating a singular writer, as it's a personal affliction in my view). The results can be found here.
So, that's a 'no', then.
'An excuse to procrastinate'. Hmm, that seems a bit harsh to me. I would wager, and I'm playing Devil's Advocate here, that you can only appreciate and understand writer's block once you've actually experienced it yourself. Perhaps it's like when a friend moans of back pain, and you nod with some sympathy but don't give it much thought. Then, when you find yourself seized with a spasm, you suddenly realise the true nature of your friend's misery.
Also, I think the term writer's block conjures up images of writers not doing anything at all; gnashing and procrastinating, avoiding their desk like the plague. People who don't believe in writer's block will tell you to sit down and just write anything. Get the rubbish out of your head. Find the good stuff again. Sounds like a neat solution but I don't think it quite fits the action required to get out of the funk.
Here's my view: it's not that the writer CAN'T write anything, it's that he/she knows that what they're coming up with has little or no value. The conflict emerges when the writer becomes too aware of every single word they're processing, and nothing satisfies their creative sense of expression. They could write a whole chapter, book or script, but still consider themselves blocked because they wouldn't be happy or it wouldn't be up to their standards, and the work quickly finds its way into the bin.
That's a terrifying prospect but one I suspect is all too real for a lot of writers. Yes, it is self inflicted and psychological - fear of failure, whatever you want to argue - but even so, does that mean that writer's block is any less real, regardless of the reasons or self-imposed embargo?
Perhaps there is no such thing as screenwriter's block. A screenwriter has no choice but to finish a script, especially if he's working in TV. You can't avoid a deadline forever, and you won't get paid until you finish what you signed up for. Even a script in development hell needs to be worked on, and a screenwriter may experience frustration and blocked moments there, but in the end, something will out. I would imagine when a screenwriter works through writer's block, the resulting script is never to their satisfaction, and quite possibly the producer's too, which could harm the writer's chances of future work.
So, writer's block? Yes, I believe it. Just ask Truman Capote, Ralph Ellison or JD Salinger. Screenwriter's block? Maybe not so much. I hope never to fall under its spell but I've certainly experienced a time where I anguished over what I was writing, deeming it not good enough to finish, or if I did, to keep it on the computer for my weary eyes only. This period emerged after a harsh run of rejections and near misses. My confidence was low, and I was desperate to find my mojo. I was writing but I wasn't writing anything good, or so I thought. I got out of the slump, but it's not a nice place to be.