Any employer that would find this question disqualifying is not an employer worth being employed by.
The interview is not supposed to be a one-sided process. Sure, the employer is usually the one in the position of more power, but it's still a negotiation preceding a contract and a contract requires both parties to agree to all terms. Your salary and benefits are the main reason you get a job, so I refuse to accept that requiring that information can reasonably be frowned upon and I've made that known when I've encountered this during interviews.
That is exactly true. That's why I've never had a problem asking about it if an interviewer doesn't bring it up. And you definitely don't want to work for a company that frowns on this type of question. They would be a bad employer, and you don't want to get into that type of employment situation....you'd just end up getting fired or quitting soon after starting there.
Absolutely, especially with smaller companies. In larger companies it might just be a problem with the particular HR person, not really a company-wide thing, but yes, adverse reaction to salary inquiries should be taken with caution... ;)
Yes. I definitely wouldn't trust a company that looked askance at such questions from applicants.