Disclaimer: I'm not really active on Math.SE, so I can't speak to site-specific issues. What follows is a commentary based on things I've observed across the Stack Exchange network. I offer it with the sincere desire that it helps.
Others, many of whom are good intentioned and contribute prolifically to the site, disagree with me. That is fine. People are allowed to have different opinions.
I'll point out that it's all well and good to say that people are allowed to have different opinions, but if the system is set up such that one side of the disagreement seems to always get its way, the other side is going to end up bitter over the bias inherent in the system.
The setup of StackExchange is such that "Closers" have an advantage over "Keep openers". On open questions, there's a vote to close option, but not a "vote to keep open" option. (The "Leave Open" option in the closure review queue only removes it from the review queue, and doesn't counteract any already-given close votes.) This means that it doesn't matter if there's 100+ people on the site who disagree that the question should be closed; so long as there's at least 5 people on the site which think it should be closed, it'll get closed. -- Those that disagree with the closure are allowed to have a different opinion, but their opinion isn't counted.
Certainly, once a question is closed there's a "vote to reopen" option. However, once a question is closed the status quo shifts (in practice). It's no longer sufficient to have a "decent" question. One must have a "good" question which has been scrubbed of all deficiencies. The hurdle to get out of closure is higher than to simply avoid getting closed in the first place.
There's also a social barrier to "vote to reopen". When a question is closed, you have a list of five (likely prominent) members of the community staring at you, telling you that this question should be closed. You know that to get anywhere you're going to have to spend emotional and relationship capital to justify reopening the question. Those five people are likely going to demand justification (probably vociferously) on the reopen call. There might be four other people who agree with you, but you know there's five that don't. In contrast, for the original close vote, there were no prominent names listed. There's only the person asking the question, who is probably a low-rep user (and whose arguments can be easily dismissed with the justification of "you're just whiny, ignorant noob"). The vote to close is thus lower effort mentally/socially than the vote to reopen.
Closure votes tend not to need extensive justification. There's not really an absolute criteria for "too broad" - it's a personal gut check. If you get it wrong, "hey, we're all human - that's why you need five votes to close in the first place!" In contrast, a vote to reopen tends to require justification: "You disagree with closure? Please explain, in referenced detail, how this question meets the criteria for being on topic. -- And it better be good, because if I find your justification lacking, I'm going to insinuate that you don't appreciate people who close bad questions and you want this place to be flooded with crap."
It's also the case that "Closers" seem to be more vocal and active in their beliefs versus the "Keep openers". The former are the ones monitoring the new question and active queues with an eye toward closing questions. And while that's laudable work to keep the site from being overrun with garbage, it does give them advantage over the "Keep openers". There isn't a "recently closed" queue for "Keep openers" to monitor (and closing a question doesn't even bump the modified time for the purposes of the active queue). It's also the case that the "Keep open" position is one more of absence of action, versus the "Closer" position of action. "Don't do things that shouldn't have been done in the first place" is not a great rallying cry, at least not in the way "We're under assault by help vampires! To the walls!" is. ("Closers are killing good questions!" might be a better one, but that opens you up to accusations of fomenting divisiveness and increasing tension.)
(I tried to be even-handed here, but this came off more anti-"Closer" than I would have liked. That's likely because the position I'm arguing is that the system is biased in favor of question closure, and I wanted to convince people who believe the two sides have equal standing.)
So, back to the main topic - how to use this knowledge to diffuse tension?
Well, I'd first encourage the "Closers" to recognize that the "Keep openers" are working from a position of disadvantage based on how StackExchange handles things. "People are allowed to have different opinions" oversimplifies. In practice, the "Closers" can mostly ignore the opinions of the "Keep openers" if they want to. The reverse? Not so much.
But the sentiment behind "people are allowed to have different opinions" is good, and I'd encourage more of it. Too often discussions on closing/downvoting/deleting devolve into thinly-veiled invective slinging, where people posting questions are painted with a broad brush, people arguing against broad closure are accused of being willing to let the site go to hell, and people arguing for broader closure are seen as trigger-happy jerks.
Both sides need to keep in mind that everyone here is trying to improve the site. That's often where I see these conversations go off the rails. Someone pulls out the "you don't care about the site"/"you just want to see the site go to hell" card, the discussion fizzles out without a satisfactory conclusion, the "Keep openers" get upset because the "Closers" can throw their weight around, and the "Closers" get upset because they feel under-appreciated and overwhelmed. Then the next meta question picks back up with the tension in the same spot it left off.