I feel like you're over-interpreting things a bit- imagining some things that can happen while blocking consideration of others, and then missing out on paths that would logically be open and saying "well, in that case we'd be doomed."
I'm pointing to a dangerous scenario - there is no certainty that the military will actually have a clique of authoritarian officers take power, with plans to subjugate parliament. But this could happen, depending on how bad our luck is. The issue is that we operate in a system that has a formalized framework for such a self-coup, granting an explicit right for the military to coup the government. The possibility of such a coup is a problem to be addressed, and I'm pointing to the fact that we lack protection against the worst-case scenario. We can try to steer against it, but our means of influence largely depend on the military agreeing to protect us against a coup.
First of all, the military isn't like to be some kind of super-secretive cabal. Finding out what people think and say to each other about politics is often just a matter of reading what they publish in known publications, paying attention to who's attending what parties, and so on. A lot of things will be matters of public record.
Sure, but such things don't give us any certain way to know their political opinions. While some people are open and very vocal about their views, some people can be apolitical or quiet before entering the upper ranks of power, and some people lie about their political beliefs in an effort to escape scrutiny from their organization and the public, especially if those beliefs are controversial. Some people change views over time, making a luke-warm democrat into a potential danger. There is no certainty our public-information based assessment will necessarily inform us of actual threats inside the military.
Second, a lot of political channels can potentially open up for you when you know what the factions you're dealing with are. There can be all sorts of ways to subtly sway key influencers to like you better, or to create situations that one faction or another can passively benefit from.
I'm not denying te have means of influence towards the military. The problem is that those means depend on the military cooperating with us, which will only happen if the military leadership is willing to cooperate with us against groups that would threaten us. The hiring and firing of officers depends on the internal decisions of the military, which are beyond our control. The military is young and progressive currently, but that can change over time in a way that is beyond our control, similar to ideological shifts in opposition parties.
There's a lot you can do to influence a political movement, as long as you have power and aren't in a deliberately hostile relationship with that movement. And if the army saw itself as needing to be isolated from us for whatever reason, then there wouldn't be a sizeable militarist party throwing its weight around and backing up our coalition government, now would there?
I agree that the leading faction in the army is supportive of us, currently. The BFP itself isn't the issue, the system giving the military the legal right to coup based on what they deem constitutional is. In the same way as an individual monarch might be fine, but the royal right to veto laws or dissolve parliament at the will is an issue. The army leadership will change over time, and the progressive leadership might simply fail to cement pro-democratic dominance inside the armed forces leading to a future problem.
