What is the ruling on fighting Sunnah practices like circumcision and growing a beard, and is it considered disbelief (kufr)?

Enmity, denial, and mockery of the Sharia (definition) constitute disbelief if the perpetrator believes that what he is fighting against is established in the Sharia. However, if he denies the legality or sunnah (definition) status of something, believing it is not part of the religion, he does not become a disbeliever by that, even if he is mistaken; because he has not denied something known to be an indispensable part of religion, but rather he is ignorant or has misinterpreted. An example of this is someone who denies the legality of circumcision or the beard, believing that they are not part of the religion.