I'm going to try to address everything mentioned here in what's hopefully some semblance of order:
I believe that we, the contributing members of the QC Stack Exchange, should have a chance to play a role in crucial future-changing decisions. The moderators should not act unilaterally on huge decisions that impact the future of our SE without waiting to hear our feedback first.
Absolutely - this is a key part of how SE runs. There are exceptions to this (e.g. suspensions) but in this case, we're referring to close reasons, in which case, yes, I agree.
Heather said "We added a "non-mainstream" close reason as well." in the chat.
Here's the chat message, a couple of days after the close reason was put into effect. As such, it was just communication about we'd already done, so I'm somewhat confused as to why it's relevant when talking about what had already happened by that point.
The moderators also say they consulted the community managers about this
To my knowledge/recollection, we actually didn't. We quite possibly talked to other site mods about this though. Assuming you're referring to the chat message above, we talked to CMs about the possibility of changing the logo and implementing the jobs page but not about the close reason.
There is only 1 answer that supports Heather's proposal, and it is from a user with 0 reputation on the QC stack exchange, who doesn't actively participate or get affected by the decision in the way the rest of us do.
Heather has also asked in a comment, for a user (with 0 reputaiton on the QC stack exchange) to write up an answer that supports her proposal.
Sure but this is irrelevant. The answerer doesn't matter - it's about the content of the post1. Please don't assume that just because a user hasn't posted anything on this site before doesn't mean they won't in the future, especially when the user is extremely active over a fair chunk of SE.
Can we not wait until we get a decent amount of feedback before making such big decisions?
I think what it boils down to here is what's meant by 'decent'. At the time of implementing the close reason, the answer supporting the proposal had a score of 6 and the answer against the proposal had a score of -3. Considering such a relatively short period of time, we figured this was indeed 'decent', especially as there were only 80-something 'avid users' (i.e. a user with at least 200 rep) on the site at the time. A call has to be made at some point and a difference in score of 9 votes seemed to be a pretty good time to make that call. It's also not that big a decision considering that it's easy to undo by clicking a button.
Can we not start making such big decisions like "custom made close options" until there is evidence that it is necessary? The comments in that question and my answer to it prove that all three examples of why the new close reason would be helpful, were invalid.
You're free to believe that comments are invalid but SE works on the majority of views and if the majority of people disagree with you that the comments are invalid then that's the viewpoint that's taken into account more. If you believe the comments are invalid then you have to convince the majority of that.
Does this mean we want the rules to be constantly in a state of flux?
If the votes are constantly in flux we wait for this to settle down.
One day "non-mainstream" question are allowed, and the next they're not?
While it wouldn't be a good idea for the close reason(s) to be in a constant state of flux, if the votes do happen to change at some point in the future, then yes, so does the close reason.
For 5 months we allow them, then suddenly someone spend 2 hours asking a carefully formatted non-mainstream question,and you send them away?
Not quite - we close the question and do what we can to get them to ask something on topic or, if possible, get an answer to their question another way, such as through discussion in chat. (i.e. same procedure for any other off-topic question) However, if something is non-mainstream, the 'answer' would tend to be along the lines of 'your reasoning is wrong [at these points] and you should read [these]' to get that fixed. If such an answer can be made, then, ideally, the question should be edited to actually ask for where the reasoning is wrong/a resource request. Sometimes an answer may not be possible of course, but that's the nature of SE - we don't answer everything.
Furthermore, at what point did you tell us that's how you make huge decisions (just by votes)? I upvoted that answer simply because it was a new user who made a lot of effort and I wanted to praise them for that, but it doesn't mean I support the idea. How are you going to separate my vote out of the others when making huge decisions?
OK, the mistake was that the question should probably have been tagged as a feature-request. Personally, I figured it played the same role as a feature request once the answers essentially became 'I agree' and 'I disagree'. As this post is the only complaint we have about this close reason (aside from the disagreeing answer to the original question), I'm also going to assume that everyone else viewed it this way. In any case, in general, although not always, voting on meta tends to signify agreement or disagreement even for discussion questions as well. Put a different way - if it looks like voting could signify agreement or disagreement, it probably does.
Furthermore, at what point did you tell us that's how you make huge decisions (just by votes)?
We probably haven't explicitly mentioned it until now but then again, how else do we determine what people actually want? Things like amount of answers/comments aren't very good because it could just be a vocal minority.
How are you going to separate my vote out of the others when making huge decisions?
We can't. I'm sorry this wasn't made explicitly clear before but at least you know now. In this particular case, it wouldn't have made a difference anyway (other than maybe an extra day or so before the close reason was implemented).
1 Having said that, the answerer is a mod on CS, so they do have the experience to back such an answer up