Often, there are questions asking for tools that solve a problem. When a user posts an answer that is "no" or "I don't think so," without a solid reference it's my opinion that these don't constitute answers. Example: 1
It's impossible to prove the absence of something, unless it can be proved that the problem is intractable. It's also difficult or impossible for the author of the question to verify that an "I don't think so" answer is correct. Given this, at best, I think these should be comments on the question.
A case where it would be acceptable to answer "no" is "Does [this complex tool] have [this feature]?" An acceptable no answer should point to either a reviewed support request from the vendor.
To clarify, after the below discussion in the comments, I am not talking about answers to bad questions that should be rephrased. For instance "Does a tool exist to solve the traveling salesman problem in linear time?" should be rephrased, "What is the lowest-order known solution to fully solve the TS problem?" Either way, the former question should remain unanswered, and comments should guide the author to edit it into a better-formed question.
I believe I've flagged "answers" like this before as "not an answer" and had the moderators reject the flag. Should there be a new flag to encourage removal of these types of answers? Or does the community find these types of answers acceptable?