Duh, but I don't consider Hiashi our enemy.
If we see Hiashi as only as our enemy, he will continue to remain our enemy. We need to consider every angle even if he's currently the big bad.
See, here's the thing: I can't see any situation where he won't treat us as
his enemy. ISC is a fairly decent power block, Goketsu is allied with ISC, and Tsunade is likely allied with Goketsu in some regard via the mutual connection to Jiraiya. The same is possibly true for Naruto. We don't really have a candidate for the hat if Tsunade doesn't step up, but we can throw some weight around. Hazou is acting head of the Goketsu, and Hazou is apparently an idealistic idiot who's expressed views diametrically opposed to Hiashi's.
In the current situation, the world is genuinely in a pretty precarious position. If Hiashi cares about anything enough to want to protect it, and if he has any beliefs at all, he has to act decisively to protect those things and to instantiate those ideals. Goketsu is a rival, and even if he isn't some flavor of xenophobe (which is, I will remind you,
the default here, on top of previous statements and actions--and given that he's been in a feud with Jiraiya, his opinion of the new blood is going to suffer emotional bleedover), this means Goketsu is a potential obstacle. Does he have any reason to believe that Goketsu will throw their weight behind him? See above comments regarding idealistic idiots and expressed ideals: courting Goketsu is not likely to succeed. This means that, even if he doesn't believe we're a threat to Leaf (xenophobe mentality default!), and even if he doesn't believe we'll ourselves treat him as an enemy (consider the current temperature of the thread, and assume he's not an idiot), it's to his benefit to try to preempt us.
(Now, he can't do anything more actively hostile, because Tsunade is there. This averts the worst possibilities. It also means that we can't count on him overplaying his hand,
and it means that if he genuinely believes we're dangerous, he's adding "might steal away the village's strongest current S-rank" to that list of possible impacts. This is not a good thing. Also, he knows about Skywalkers, and has just been reminded of their impact on warfare. Skywalkers currently belong to Goketsu, not Leaf. This is also going into his threat assessment.)
Hiashi was planning to make a bid for the hat before, so he's more prepared. Hiashi has more resources and more connections, including more people to implement any plots. Hiashi isn't dealing the unfortunate effects of being a foreigner. Hiashi knew about this before we did, by virtue of being in the room where it happened. And Hiashi is already acting to undermine us, just by virtue of being a basically intelligent person.
And you think now is a good time to hold out judgment? Sorry, but if you wanted to be in a situation where Hiashi wasn't some flavor of enemy, then you needed to press for different actions earlier. We don't live in that branch of the timeline.