Even if technically you're correct, in the best possible scenario it'll take time to get that money back. In the worst case scenario you get involved in a tax dispute that can drag on for however long they can afford to. Meanwhile you don't have a job.

I was fired from my "contracting" job, and the state eventually ruled that I was technically an employee. But I had to wait the longest 6 weeks of my life to find that out, and what if they had not? Or what if they ruled against me, and I had to appeal it? What if my former employer retaliated in other ways? I would have been even more screwed than I was.