From my view bitcoin is a legal currency, because it evolved to support the banking system that operates under the governments. Later with its high potential, it reached a value that gained the attention of people and governments around the world. It is not used for anything bad than few exceptions which makes its legitimate.
It's totally legal with all Bitcoin and cryptocurrency users for sure. The only people who don't think it's legal are people who are supported by the banks and the goverments which were trying to make the crypto market disappear.