I find arguing over free will to be a little pointless, because determinists tend to be people who simply don't understand the concept of emergent properties. It's why things like "the ability to do otherwise" that you mention don't really matter to them - if the universe is at base random and chaotic rather than deterministic, it's still not something that you have control over. Basically, free will is not a property of the universe at a basic level - it just emerges in certain complex systems. It's like "life" or "consciousness" in that respect. But emergent properties are difficult to explain, and a lot of people would rather disbelieve in them rather than admitbto the reality of something they don't understand. Hell, I've seen people argue that consciousness and even life are illusions rather than face having to admit that the world contains things science can't easily explain.