I'm sorry if this response comes across as overly negative (feel free to vote as your conscience dictates) but it strikes me as a practical concern that many of the other answers are skirting around.

I agree with the other answers saying that we shouldn't change our policy on this but have a slightly different slant on why:

Our current policy is very clear, easy for new users to understand (even if they disagree with it) and relatively simple (if not always painless) to enforce.

Any alternative to this policy, however well intentioned (and perhaps both sensible and justifiable in the abstract), will be much less clear, more contentious and harder to enforce.

Presuming that we don't declare guessing at systems to be acceptable in every circumstance (something that no one is advocating) any change to the current policy would mean attempting here on meta to draw a line somewhere as to when guessing was and was not acceptable.

The drawing of this line, however clearly stated it was here in meta, would in practice almost certainly lead to (potentially protracted and unhelpful) disagreements on the main site and require heavier moderator intervention.

If we say that 'we'll only guess a system when we're 100% certain that we're right' there will still be rare occasions when the most experienced users turn out to have been wrong, despite all of the cues. The much bigger issue however, is that, if we legitimise guessing in any form, less experienced users will also be empowered to guess when they are '100% certain' and they may not be as well equipped to make such an assessment.

We're already in a position where new users occasionally guess systems inappropriately - but currently the response 'Sorry, we never guess systems here', while potentially annoying, is pretty clear. Saying instead 'Sorry, we do sometimes guess systems here but you should not have done so in this instance' is going to be much trickier to enforce in a way that people find to be consistent, fair and reasonable (and don't take personally).

A categorical ban on guessing systems is obviously impersonal. Allowing some guesses and not others is always going to feel more personal to some users (whether or not it actually is).

I agree with the other answers saying that we shouldn't change our policy on this but have a slightly different slant on why:

Our current policy is very clear, easy for new users to understand (even if they disagree with it) and relatively simple (if not always painless) to enforce.

Any alternative to this policy, however well intentioned (and perhaps both sensible and justifiable in the abstract), will be much less clear, more contentious and harder to enforce.

Presuming that we don't declare guessing at systems to be acceptable in every circumstance (something that no one is advocating) any change to the current policy would mean attempting here on meta to draw a line somewhere as to when guessing was and was not acceptable.

The drawing of this line, however clearly stated it was here in meta, would in practice almost certainly lead to (potentially protracted and unhelpful) disagreements on the main site and require heavier moderator intervention.

If we say that 'we'll only guess a system when we're 100% certain that we're right' there will still be rare occasions when the most experienced users turn out to have been wrong, despite all of the cues. The much bigger issue however, is that, if we legitimise guessing in any form, less experienced users will also be empowered to guess when they are '100% certain' and they may not be as well equipped to make such an assessment.

We're already in a position where new users occasionally guess systems inappropriately - but currently the response 'Sorry, we never guess systems here', while potentially annoying, is pretty clear. Saying instead 'Sorry, we do sometimes guess systems here but you should not have done so in this instance' is going to be much trickier to enforce in a way that people find to be consistent, fair and reasonable (and don't take personally).

A categorical ban on guessing systems is obviously impersonal. Allowing some guesses and not others is always going to feel more personal to some users (whether or not it actually is).