I don't think bitcoin will EVER be illegal. Trading/exchanging bitcoin for USD could become illegal, but trading, spending, mining, bitcoin will never be against the law in the US.
I agree with this, I also think that (hopefully) the government will realize the potential in the future of cryptocurrency and will regulate as opposed to making it illegal. While they wouldn't directly benefit from it, the indirect benefits of adoption by a large number of their constituency is a big indirect benefit if growth of cryptocurrencies continues.