Allah, may He be exalted, has instructed His believing slaves to love one another and to take one other as friends, and He has instructed them to hate His enemies and regard them with enmity for the sake of Allah. He has stated that friendship can only be among the believers and enmity is to be between them and the kaafirs; disavowing them is one of the basic principles of their faith and is part of perfecting their religious commitment. There are very many verses, hadeeths and comments of the early generation to that effect.
For example, Allah, may He be exalted, says (interpretation of the meaning):
“O you who believe! Take not the Jews and the Christians as Auliya (friends, protectors, helpers, etc.), they are but Auliya to one another. And if any amongst you takes them as Auliya, then surely he is one of them. Verily, Allah guides not those people who are the Zalimoon (polytheists and wrongdoers and unjust)”
“Verily, your Walee (Protector or Helper) is Allah, His Messenger, and the believers, - those who perform As-Salat (Iqamat-as-Salat), and give Zakat, and they bow down (submit themselves with obedience to Allah in prayer).
And whosoever takes Allah, His Messenger, and those who have believed, as Protectors, then the party of Allah will be the victorious.
O you who believe! Take
not for Auliya (protectors and helpers) those who take your religion for a
mockery and fun from among those who received the Scripture (Jews and
Christians) before you, nor from among the disbelievers; and fear Allah if
you indeed are true believers”
The Prophet (blessings and peace of Allah be upon him) explained that love for the sake of Allah and hate for the sake of Allah are among the signs of faith. Abu Dawood (4681) narrated from Abu Umaamah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever loves for the sake of Allaah and hates for the sake of Allaah, gives for the sake of Allaah and withholds for the sake of Allaah, will have perfected his faith.”
Classed as saheeh by al-Albaani in Saheeh Abi Dawood
Al-‘Allaamah Abu’t-Tayyib Siddeeq ibn Hasan al-Bukhaari (may Allah have mercy on him) said in al-‘Ibrah (p. 245):
As for the one who praises the Christians and says that they are people of justice or that they love justice, and often speaks highly of them in gatherings and speaks ill of the sultan (Muslim ruler) and the Muslims, and attributes justice to the kuffaar naseefah and says that they free of injustice or oppression, the ruling on the one who praises them in this manner is that he is an evildoer who is disobeying Allah and committing a major sin, from which he has to repent and regret it, if he praises the kuffaar themselves regardless of the kufr (disbelief) that they follow. But if he praises them because they are disbelievers, then he is also a kaafir because he has praised the kufr that they are following.
Shaykh ‘Abd ar-Rahmaan al-Barraak (may Allah preserve him) said:
The one who believes that the Jews and Christians are following a sound religion is a kaafir, even if he follows all the laws of Islam, and he is rejecting the general meaning of the message of the Prophet (blessings and peace of Allah be upon him).
Based on that, mentioning the good qualities of the kuffaar by way of praising, admiring and respecting them, is haraam because that is contrary to the rulings of Allah concerning them. End quote.
Indeed, Imam an-Nawawi (may Allah have mercy on him) said, discussing the phrases that constitute apostasy:
If a teacher of boys says: “The Jews are much better than the Muslims, because they give the one who teaches their boys all his rights,” he has become a kaafir thereby.
End quote from Rawdat at-Taalibeen, 10/69
If, along with reviling the Muslims and praising the kaafirs, he also wishes that he was one of them, then he is a kaafir who has gone beyond the pale of Islam. He should be asked to repent and he should be taught his religion; if he repents (all well and good), otherwise he is to be executed as an apostate by the ruler.
See also the answer to question no. 6688
And Allah knows best.