Rambam rejects Chazal because he was a rationalist

 Shomer Emunim HaKadmon (1:13): It is quite obvious to us and is clearly stated in the gemora and medrash in many places that there is a power to names and amulets to do amazing things e.g., Shabbos (61a) and Yevamos (49b)…Rashba (1:220). Nevertheless, the Rambam denies that this is true and strongly ridicules those who believe in the power of names to do anything. We see this in Moreh Nevuchim (1:61–62). Thus, he does not find the testimony of the gemora credible. It is also known that our Sages received traditions concerning demons and witchcraft as is well known from the gemora and medrashim. Nevertheless, the Rambam decided that they are nonsense and stupidity and that all who believe that they are real but the Torah has prohibited them is a fool and idiot and is included amongst the ignorant women and children (Hilchos Avoda Zara 11:16)... Even though the issue of magic is mentioned in the Torah itself in a number of places - nevertheless the rationalists reject their validity and produce far-fetched explanations to these verses in order not to violate their rationalism. They are not concerned with the words of our Sages that are clearly stated in a number of places which clearly acknowledge the reality of demons and magic. Their rejection of these things is that according to the rationalistic understanding it is simply impossible that these things exist. This is the approach of the rationalists. They will simply not accept the validity of anything said by our Sages which contradicts rational human understanding…

Rambam (Tefilin 5:4) It is a universal custom to write the word Shaddai (Almighty) on the other side of the Mezuzah, opposite the blank space between the two sections. As this word is written on the outside, the practice is unobjectionable. They, however, who write names of angels, holy names, a Biblical text or inscriptions usual on seals, within the Mezuzah, are among those who have no portion in the world to come. For these fools not only fail to fulfill the commandment but they treat an important precept that expresses the Unity of God, the love of Him, and His worship, as if it were an amulet to promote their own personal interests; for, according to their foolish minds, the Mezuzah is something that will secure for them advantage in the vanities of the world.*A reproof to those who sell Mezuzoth to be worn as amulets ! 

Avoda Zara (11a) When Onkelos the son of Kalonymus became a proselyte, the Emperor sent a contingent of Roman soldiers after him, but he enticed them by citing scriptural verses and they became converted to Judaism. Thereupon, the Emperor sent another Roman cohort after him, bidding them not to say anything to him. As they were about to take him away with them, he said to them: ‘Let me tell you just an ordinary thing: In a procession the torchlighter carries the light in front of the torchbearer, the torchbearer in front of the leader, the leader in front of the governor, the governor in front of the chief officer; but does the chief officer carry the light in front of the people that follow?’ ‘No!’ they replied. Said he: ‘Yet the Holy One, blessed be He, does carry the light before Israel, for Scripture says. And the Lord went before them . . . in a pillar of fire to give them light.’ Then they, too, became converted. Again he sent another cohort ordering them not to enter into any conversation whatever with him. So they took hold of him; and as they were walking on he saw the mezuzah which was fixed on the door-frame and he placed his hand on it saying to them: ‘Now what is this?’ and they replied: ‘You tell us then.’ Said he, ‘According to universal custom, the mortal king dwells within, and his servants keep guard on him without; but in the case of the Holy One, blessed be He, it is His servants who dwell within whilst He keeps guard on them from without; as it is said: The Lord shall guard thy going out and thy coming in from this time forth and for evermore.’ Then they, too, were converted to Judaism. He sent for him no more.

Zohar (3 266b)  R. Abba further discoursed on the verse: “The Lord shall keep thy going out and thy coming in from this time forth and for evermore” (Ps. CXXI, 8). He said: ‘That God shall keep thy going forth we understand; but what need is there to say, “thy coming in”? For when a man goes into his house he is in no danger? What it means, however, is that he who affixes the holy sign to his house with the words of the Holy Name is protected against all danger. The one who dwells at the door of his house accompanies him when he issues forth, and when he returns it proclaims before him: Have a care for the honour of the image of the Holy King-all this on account of the Holy Name which is impressed on his door, so that not only is a man protected in his house, but God protects him both when he goes out and when he comes in, as it is written, “The Lord shall keep thy going out and thy coming in”, etc. But as for the evil spirit that abides between the doorposts, woe to the man who does not know how to guard against it by impressing on the door of his house the Holy Name that it may be with him, for this spirit has three hundred and sixty-five assistants, one for every day of the year, which accuse him above and below, trying to mislead him by day and troubling his dreams by night. When he goes out they accuse him; when he comes in they place their hands on his shoulders and say: Woe to So-and-so who has thrown off the control of his Master, woe to him in this world and in the world to come! Therefore the sons of the true faith should be stamped throughout with the impress of their Master to scare away all the sides of the “evil species”, that they may be protected in this world and the next.’