Christians, both Evangelical and Liberal, are united in that they hate the idea that one’s experience of God can turn on them. That’s part of the reason why they don’t engage individuals with mental illnesses on a deeper level. Some thoughts:
This idea calls into question God’s power. You would think if a god was as just and powerful as he is advertised the least he could do is get communication right. Christians are quick to point out that hostile voices coming from God are from the devil or one’s mental illness but if these voices so easily overpower positive things God is trying to say it says something about his sovereignty.
Saying experiences of God can turn against you erodes the child-like trust in God. Second-guessing everything God tells you is not a recipe for a healthy faith. Christians know this so they make trusting God fully the default state. Only a tiny minority of Christians will have these negative experiences so there is no point in sacrificing the majority’s trust experience for an often-scorned minority.
Calling into question the “personal relationship with God” paradigm makes the faith a lot less attractive. One of the most beloved aspects of the Christian faith is the idea that a loving god will walk beside you and guide you. The idea that this experience can turn against you begs the question, are positive experiences from God really from God in the first place or are they just windfall from one’s functioning mental health? Mentally healthy people have voices in their head as well but they generally tell them to do positive and pro-social things. Is “experience of God” just beautifying these voices? And once you realize it’s all in your head (and subject to the vagaries of your mental health) your Christian experience will likely become more hollow.
The idea that one cannot trust their experience of God throws a rod in the idea of seeking God’s direction. If you have veto power over everything God says doesn’t that make you—not God—the one ultimately in control? And what do you fall back on when you override “God’s voice”? The church? Your church’s interpretation of the Bible? A helping professional? These options are better but you might be seen as making a mistake by pursuing them instead of “God”.
The idea that your experience of God can turn against you runs counter to the idea that God will never leave you or forsake you. Christians say it just “seems like” God is forsaking you but he really isn’t. Unfortunately what “seems like” it’s true is often based on eons of actual experience while what “is” is based on dogma. People with mental illnesses are often marked by their experiences—for them there is no pie-in-the-sky “is” any more.
I think it’s very healthy for people—especially those with mental illness—to never take God’s voice seriously but many of us have been brought up in religious environments where we were told to do the opposite.