This video by Sheikh Bilal Philips answers some
questions like: "If it says such and such in the Qur'an is halal or haram,
is that enough to act upon?"
and "Can you get your hand cut off for stealing a pencil?"
It is absolutely wrong for a Muslim to say: "I will follow the Qur'an only,
not the Sunnah." For those who go by this, ask them: "Do you also
avoid the part of the Qur'an that tells you to obey Allah's Messenger (S)?"