Is a Muslim who does not follow the teachings of Islam worse than an atheist?
Question

                Is it possible to be a "non-practicing" Muslim? Basis for question: A friend of mine married a "non-practicing" Muslim from Iraq. While he drinks wine and or spirits, and married a kufaar, he will not eat pork. My impression is that a "non-practicing" Christian would be considered to be apostate, or worse than an infidel.
Praise be to Allah.
    The Muslim is obliged to adhere to the teachings of his 
    religion and perform the obligatory duties of praying, fasting, honouring 
    his parents, upholding the ties of kinship, speaking truthfully and other 
    duties that Allaah has enjoined upon him. 

    He must also avoid that which has been forbidden, such as 
    zina (unlawful sexual relations), riba (usury or interest), drinking 
    alcohol, disobeying parents, lying, treachery, consuming people’s wealth 
    unlawfully and other forbidden things. 

    This is obligatory upon every Muslim. Whoever adheres to that 
    will be close to Allaah and beloved to Him, and is promised admittance to 
    Paradise and being honoured by Him. 

    Those who neglect the obligatory duties or commit forbidden 
    actions fall into two categories: 

    1 – Those whose sin reaches the level of kufr (disbelief) and 
    shirk (associating others with Allaah), such as mocking the faith, insulting 
    Allaah, insulting His Messenger, denying any of the well known tenets of 
    Islam, or regarding as permissible something that Allaah has forbidden, such 
    as regarding wine, adultery or pork as permissible. Whoever does that is an 
    apostate from Islam, but if he does that out of ignorance or negligence, 
    then he should be taught, advised and reminded, so that he may repent to 
    Allaah. If he persists in that after being taught, then he is an apostate 
    who is beyond the pale of Islam. 

    2 – Those who commit some sins that are not regarded as kufr 
    or shirk, such as adultery or drinking wine, without regarding that as being 
    permissible. If such a person repents, Allaah will accept his repentance and 
    turn his bad deeds into good deeds. But if he persists in his sin, then 
    Allaah warns him of the painful punishment on the Day of Resurrection, and 
    of punishments in this world, such as poverty, sickness, humiliation and 
    defeat, as well as having the hadd punishment carried out on him when 
    committing some crimes, such as drinking alcohol or committing adultery, if 
    it is proven that he committed the crime, and subject to certain conditions 
    that we do not have room to discuss here. 

    The Muslims’ duty towards those who commit sin is to advise 
    them and call them to repent, and remind them of the danger of sin and the 
    evil consequences thereof, as well as hating them because of their sin. 

    The obedient and the disobedient are not equal before Allaah, 
    or before His believing slaves, as Allaah says (interpretation of the 
    meaning): 

    “Shall We treat those who believe (in the Oneness of 
    Allaah –– Islamic 
    Monotheism) and do righteous good deeds as Mufsidoon (those who associate 
    partners in worship with Allaah and commit crimes) on earth? Or shall We 
    treat the Muttaqoon (the pious) as the Fujjaar (criminals, disbelievers, the 
    wicked)?”

    [Saad 38:28]
But if a sinner does both 
    good and evil, and does both acts of obedience and acts of disobedience – 
    and chief among goodness is belief in Allaah – then the justice and mercy of 
    sharee’ah dictates that his good deeds should not ignored or wasted, and he 
    is not to be regarded the same as those who disbelieve in Allaah 
    altogether. 

    With regard to a Muslim marrying a kaafir woman, this is 
    haraam, unless she is a Jewish or Christian woman, for Allaah has allowed 
    marriage to them, because of the possibility of their being guided to Islam 
    and because these religions share with Islam the belief in Allaah, the 
    Prophets and Messengers, and the Last Day. The marriage of such a woman to a 
    Muslim may lead her to seek the truth and encourage her to give up her 
    disbelief in Muhammad  (peace and blessings of Allaah be upon him) and 
    his message. 

    To sum up: 

    The Muslim who leaves his religion altogether is as bad as an 
    atheist, or worse. 

    As for the Muslim who believes in the basics of Tawheed 
    (Oneness of God) and Islam, but he commits major sins and abhorrent actions, 
    he is undoubtedly better than a kaafir and atheist – despite his 
    shortcomings – because the good deed of Tawheed (believing in the Oneness of 
    Allaah) is the best of all good deeds, and he has done that. But he is 
    warned of a painful punishment in this world and the Hereafter for the sins 
    he commits, if Allaah does not bestow His mercy upon him and forgive him. 
And Allaah knows best.