That is true that concepts of morality are also connected to relational motivations as well as the reward/punishment - in varying degrees depending on the religion and the individual interpretation of the religion. That also tends to occur on two levels - the theological level of obeying and having a relationship with god and then the social level of relationships and punishment/reward for staying in line with the requirements of the social group.
I spent well over three decades inside religion - all my social interaction, my family, even my employment and education for many of those years centered around religion. This was not just immersion, but continual study of this core religion as well as comparisons with other religions. I'm still what could be called a somewhat closet agnostic/atheist because repercussions would be problematic. I spent so many years studying religion and defending it as well, but there were certain aspects I could not see until I became an outsider.
If you have spent your life inside and have never experienced religion as an "apostate", there is one level that can be impossible to see. On the inside there is the compassion of Jesus and the hope of eternal peace with loved ones which requires a process of deep grieving to let go of. There are also anxieties about eternal punishments and how that effects the way specific people/sinners are viewed, judged, and valued in the present concrete world. The way the "lost", the "backsliders", and "apostates" are viewed is with great distrust. The assumption that you cannot be moral outside the religion, or that you are not "born again", or even "alive in Christ" makes you something less than fully human.
People who have loved and trusted you all their life are torn between the requirements of theology for how you must be viewed, and their own personal history of love and trust for you. It is difficult to reconcile without forcing the outsider into the box of "rebellion" or "distraction with the cares of the world". If you are conscientious and only desire peace within oneself and with others, you make no sense as an outsider to religion. You must be horrible things and you will be called those horrible things by people on the inside. Some will do it out of certainty and others out of confusion. And in religions where you are viewed to be destined to be tormented forever and yet are expected to not be offended by that in any way, but to make every allowance for that belief and not reciprocate with any negativity, the potential for a healthy relationship is ruined. It would be a rare atheist/agnostic who would ever see a believer of any system as deserving of such a horrific fate. They might be rude and make fun or even be downright mean, but they would never cross that line.
I would not personally want to take someone away from their religion because people are too complex and it is too deeply intertwined and it takes too much effort and even grief to let go. That makes it a personal choice that comes from inside which should be respected. I would never impose that on someone, but I would ask each person inside a religion to respond to those outside based on your model of compassion who for Christianity is Christ, an advocate for humanity and not a punisher.