Exactly, these days Kamen Rider is more on the greyish side than black & white. Ever since Ryuki, Riders either fight for others, themselves or just evil. It's sort of like two sides of a coin. While some Riders are good the others have to be evil.
Not to mention that the original Kamen Rider was suppose to be evil, until he escape before he was brainwashed, thanks to his teacher.