The root problem is too many churches are social groups of religious thinkers, instead of believers in Christ who are seeking the very real spiritual walk with Him.
That spiritual reality is not academics, not comparative religion, nor a feel good session.
It is a state where believers congregating, all fall into fellowship with Him in unison, and God the Holy Spirit very really begins to grow their human spirit, each by their respective spiritual gifts, and He begins to sanctify them,...improving them from their scarred souls, even an everyday worldly thinking soul, into what He has planned from eternity past to provide for their spiritual maturity to be able to perform in all eternity future when they are called before the bema seat for their future eternal rewards.
Islam isn’t crap, not even a notion, ... compared to what God provides in even a 5 second fellowship with Him for an eternally future reward.
The walk with God is not a dead relationship. It is very much living and alive. Those who don;t have a living relationship with Him, need to return to Him first and let Him guide their walk. It is the simplest most fulfilling reward they will ever have and is even possible, because God is the one who has planned all of it from eternity past.
Many of the main line churches have denied the essential Christian doctrines as we know them to be. The centrality of Christ is often simple lip service...He is no longer “exclusive”....may doubt the authority of scripture and seek man to substantiate what they believe rather than knowing why they believe what they do...and further they deny the inspiration of Scripture.
All manner of various eastern practices..yoga, tm and the like have been accepted into the churches as well... So as one author wrote...” I’m not shocked that pagans would unite with pagans.”
Even so...when it comes to muslims years and years of brainwashing it is no small a matter to bring them to Christ...and even harder still for them to let go of Islam even after they have a conversion....many will incorporate the two.