There are three types of people that are against the honorable science of Kalaam: complete heretics, some deviant innovators, and imitators of literalists that associate themselves with Islam:
As for the heretics, one would expect nothing less from them, since they have no one to expose their blemishes and blind imitation of habits other than the specialists in Kalaam. Indeed, it has been said:
كل العداوات قد ترجى مودتها … إلا عداوة من عاداك في الدين
All enmities are hoped to turn to affections
Except the enmity of religious inclinations
As for the innovators, especially the Muˆtazilah and those who deny predestination, they did not generally reject Kalaam as a scientific field, but engaged in it. They were only against Sunni Kalaam.
As for the literalists, they are of three kinds:
1- Those who say Kalaam has no basis in the religion because neither the Prophet nor the companions engaged in it. They also argue based on misguided interpretations of certain statements in the Qur’aan or in hadith narrations. This group (of literalists) is the most harmful to the common people among all groups against Sunni Kalaam. This is because they appear to (but not actually) find justification in the religion itself for their objections and convince people of their misguided interpretations.
2- Those that believe that the science of Kalaam is the foundation of the religious sciences, but do not admit it because unlike some others they did not try to learn it, or tried but were unable to master it. Hence, they become against it out of arrogance and envy.
3- Foolish imitators who follow one of the groups mentioned.
With regard to the first type of literalists, it is in fact known that there are no authentic narrations from the great scholars that attack or speak against this knowledge or science. And how can someone who claims to be a Muslim object to a science which:
- Establishes and proves that Allaah is One and has attributes of complete perfection and refutes that Allaah has any flaws and declares Him clear of the wrong ideas that the deviants and blasphemers ascribe to Him?
- Proves and affirms Prophethood based on miracles and on the same bases shows the difference between a prophet and a liar?
- Establishes what an accountable person is accountable for, and when and how?
What trace of belief is left in someone who objects to this science and encourages people to avoid it?
Source: Muqaddimaat al-Maraashid, Ali ibn Ahmad As-Sabtiyy (614/1217), Maktabah Al-Thaqaafah Al-Deeniyah, 2008, p. 25-26
Sunni Answers 
Salam Alaykum,
With respect to the groups that reject predestination and/or claim that the creation are the originators of their actions, what have the scholars said concerning their level of deviation?
It would seem to be (on a superficial reading) that they are on the same level as gross anthropomorphists in denying Allah as He truly is, but have any scholars said that they are actually outside the fold of Islam?
Wa Salam
If that is what they actually believe, i.e. that their actions are not created by Allaah, then they are mushriks, since they have named themselves partners of Allaah. This is our Sunni belief regarding this group. However, the actual practical takfiir for specific people in a court depends on the clarity of statements made. There are a lot of statements that Qadaris may make that can be interpreted to have a sound meaning. Moreover, a lot of common people fail to understand fully the meaning of what they say on such intricate issues as accountability and predestination. Hence, unless the statements made are very explicit, you may find a lot of scholars being careful with making explicit takfiir for the Qadariyyah. After all, people may be associated with them without fully understanding the meaning of what their leaders say. However, the Sunni scholars agreed that the Qadariyy scholars are kuffaar, since they do understand what they are saying. AbdulQaahir Al-Baghdaadiyy, Abu Mansuur, said: “Our companions said regarding those who disagree with us — such as the Qadariyyah [who deny predestination and that Allaah creates our actions – Ed.], the Khawaarij, the Raafidah, the Jahmiyyah, the Najjaariyyah, and the Mujassimah (anthropomorphists) — that they have no valid obedience to Allaah, because they mean their obedience to be for something worshiped that is not the true God as far as we are concerned.” (Usuul Al-Diin, P. 267)