Why are apostasy, paganism, and atheism fought against if Islam has affirmed freedom of belief?

Islam does not sanction freedom of belief. Rather, it commands and imposes a sound belief system on people, making it obligatory to affirm God's oneness, to be sincere in devotion to Him, and to adhere to His religion. The Quran and Sunnah have clarified the obligation to adhere to God's law, and that a person has no freedom to choose another religion, or to do what God has forbidden, or to neglect what He has commanded. A Muslim must remain steadfast in the religion of Islam, affirm God's oneness in worship, believe in His Messenger Muhammad, peace and blessings be upon him, adhere to his law, perform the pillars of Islam, and avoid what God has forbidden. Whoever changes his religion, if he does not repent, he is to be killed. A Muslim does not have the freedom to abandon the truth and embrace falsehood; rather, he is obligated to remain steadfast in the truth and abandon falsehood.