Indeed that a forums that is focused on Sinodefense is going to attract Pro-China users and that they will want to express that.
The sticky point about that is the nature of specific examples of Pro-China voicing. The sort of posts that are bluntly just like "you're opinion does not matter" or "Japan's opinion does not matter".. things like that break done intellectual and potential for enlightening discussion. Of course being saying that, depending on the topic at hand "you're opinion does not matter" may actually be valid. It goes case by case on that judgement. I would submit that in the Taiwan thread a flat out "Japan's opinion does not matter" is not logically valid.
What makes it difficult is that actaul PRC policy itself is very controversial and so Pro-China users will make whatever argument, logical or not, to stamp down on opposition. Again, its very slippery slope here because of the case by case reality of it. An overhead principle/guideline of forum moderation is not nimble enough to navigate through the case by case nature of each topic and each post by each poster that brings with themselfves an air of position. Literally even the meaning of the same exact statement but said by diferrnt posters can bring out different meaning behind the literally same exact sentence even.
If a principle of other forum boards have their established bias with still all variety of threads available, then yeah, I think SDF very well will go the same way that the asia and china defense section at PDF ended up turning into. The static will wash out quality and the custom and behavior molded for the purpose of preserving that quality.
At a certain level of impasse on certain geopolitically sensitive topics what you describe is inevitably going to be the endgame.
That is why when I'm on other forums I almost always do not even engage on topics that I know I hold different political opinions on, especially if I know it is something that the majority of the userbase holds very strong opinions on.
At a certain level it isn't even about etiquette but also common sense and a good use of my time.
If this forum were as much of an echo chamber as some other national forums, frankly there are some members who would have long been instant banned just a couple of posts into their stay, without being given the leniency that they were.
This isn't to say that we should compare SDF "downwards" to other forums or lesser quality, but at the same time it does mean that I don't think depriving SDF of having a space for its pro-China userbase that other specific military forums have for their pro-US, pro-UK, pro-India, pro-Japan, pro-Korean, pro-Pakistan to discuss non-military matters as well.