Stress in a job situation is like building a fortress over many months and getting invaded. You know the layout of the terrain like the back of your hand and you can focus on the problem.
Stress in an interview is like being air dropped into an enemy fortress. It is hard to know where to turn and you spend as much energy trying to suss out the layout of your new environment as you do reacting to your adversary.
This completely contradicts the argument that a candidate who has difficulty handling interview stress will not have the ability to handle any stress. I can't speak for everyone who gets nervous during interviews, but in my case it's due to the combination of the uncomfortable environment, lack of access to tools I've grown to rely on, and an awareness of how fickle people's opinions are.
Then you are doing it wrong. There are different types of stress. Holding up well under "stress" is a misnomer, as someone can hold up well under one type of stress, and completely fall apart in another situation entirely.
What you are testing for is the ability to handle the stress of interviewing. If anything, you are hiring for people who can more easily leave.
While it's appropriate to test for situations where stress is a factor, it's equally important to realize that talking to a customer and doing pre-sales and an interview are about as far apart as possible on the stress meter. One hardly equates with the other.
And that's coming from someone who enjoys interviews, because I'm almost always smarter than the other guy (and it's usually a guy) interviewing me. Every job interview I've had has resulted in an offer.[1]
But their unique and outlandish nature sets them so far out of anything experienced in a job situation, except possibly for sales. Trying to give them the meaning you're going for is rather pitiful given you're so earnest!
[1] For similar reasons, I generally decline to interview prospects, because I'm afraid I judge too narrowly.
No.
If you're only willing to consider people who can somewhat function under artificial pressure, then you're passing up a lot of top-notch candidates for very bad reason.
Freezing up in interviews would probably be a red flag for a job where you're doing cold calls or something like that. I wouldn't accept that kind of job, let alone interview.
Then you're like the guy who punishes interviewees because they didn't estimate the number of sewer ducts in New York correctly. Interviews can cause anxiety and stress to an extent that a typical employee may never encounter in their work.
A client meeting, code review, or dispute with a manager can be stressful, but you can answer from a position of strength. You know your code, have reasons for your decisions, and have met some standard to get the job. Interviews may be less demanding, but for some people it's a huge problem that there's no solid place to stand.
And empirically, we endlessly observe very nervous people at interviews that do not exhibit nervousness in meetings (after getting the job).
We know that people behave differently in interviews; I suggest using that behavior to predict behavior in non-interview situations is noisy at best, and probably entirely random.
Stressful situations happen a lot more than never in the real world (and sometimes they even involve talking to people, like customers) -- I don't want to have coworkers who can't handle that.