Ironwood newest actions make sense and here is why:
Many people saying bad writing and sure some of these things could have been better but what many seem to forget is that emotions still exist as well. Emotions like anger, hate, fear and exhaustion which all becomes worser with every hour they spend without sleep. We even saw Ironwood destroying his desk full of anger after again some of his plans doesn't work and this is his problem.
Than ever he plans something Team RWBY's actions interfer his and because of this he sees them as a threat and not only as traitors. He believes that his plans will only work if Team RWBY is out of the picture and this is his big mistake which ruins his plans.
All what Ironwood wants is the Winter Maiden so that he can lift up Atlas with the staff of creation and save its people. He doesn't care about Mantle because he thinks that Mantle's people can't be saved with the relic along with Atlas.
The plan itself already is very stupid if we think about it realistically because the people can't breathe if they are to high in the air, their resources like water, food, medicine and dust will run out and they won't get any new because Salem's forces will just destroy the airships and Salem could also try to shoot the flying island from the downside to destroy Atlas. Sure we don't know how much the Staff of Creation can do against it but we also don't know how much destruction the Sword of Destruction can do then it comes to destroying an enemy and Salem would move on if she can't get Atlas immediately.
But since Ironwood truly believes his plan would work, he needs the Winter Maiden at any cost.
Normally he would offer Team RWBY help like more airships for protection or for the evacuation as an exchange for the Winter Maiden which they might even take to protect the people of Mantle. But because of their betrayal, all their interfering in his plans and also the strong negative emotions, he believes now that working with them will only ruin his plans again and if they doesn't give Penny free willingly, he will take her by force by using Mantle as a hostage against them.
He knows that the SDC airships are actually good and not a threat to Atlas at all but he also knows he needs to do something before it's to late for his plan to work and using Mantle as a hostage is his only option right now. Ironwood doesn't know that Penny and the others are at the Schnee Manor otherwise he could send his forces there instead of using Mantle as a hostage.
This is his last chance to fulfill his plan and since he believes that without his plan everybody will die and only Atlas can be saved with his plan, Mantle is already lost for him. So using Mantle's destruction against Team RWBY as an ultimatum to save what he believes can be saved makes totally sense.
He could achieve his goal without all of that but after all what happens he is no longer able to understand that.
Ironwood is not a bad person. He trys to save people. He really believes what he does is right but after all the things that happen to him, he is no longer able to understand what is right or wrong. Back in the past he wouldn't do things like that but in the past nothing like all of this bad things happen to him to learn from it.
Team RWBY also isn't good or bad. Their biggest mistake was to not trust Ironwood with the truth at the beginning. They had a good reason to not trust him after all the bad things they saw in Mantle but they waited to long and this is what caused all of that.
None of them is good or bad. Both of them did just the wrong thing in the wrong moment because of mistrust and what they believe is right or wrong, which in the end made everything worser.
This is normal human behaviour, feeling and thinking.
