All have some sort of mental illness of one sort or the other. Conversion put's us on the path of renewing our minds, to renovate out minds, Romans 12&c. This doesn't mean that all mental issues will then be healed due to salvation.
Note Titus 3:5; 2 Corinthians 4:16; Ephesians 4:23; Colossians 3:10.
Those who attack other believers due to their mental issues are simply showing us they too are mentally ill. Just pity their deficiency and ignorance, they're sick and this is how their personal sickness manifests itself. They, in their alleged solid mental state and conversion (alleged) are incapable of showing God's grace to others. They need more mind renewal, renovation. Pray for them.
Many pastors have been noted as to having mental illness. Charles Spurgeon suffered from depression. There are more. Many believers suffer from various forms of mental illness. This is a result of the fall so we are all deficient mental health wise in one way or another.
D. Martyn Lloyd-Jones has a wonderful sermon series that will be of great help to those who suffer spiritual depression.
God didn't promise to heal all of our maladies, whether mental or physical. Don't get caught up in the lie that He does. It is appointed for us not only to believe, but to suffer as well, Philippians 1:29 &c. Christianity isn't escape from suffering and reality.
My late brother suffered from schizophrenia, others in my family with depression and anxiety. Some have higher degrees of suffering, some lower degrees and lesser mental illness.
If we'd all see the human race in the same boat, spiritually (which is our psyche, by the way) and the Gospel of Christ our only hope, we would do well.
Hang on all converted, there is a new world coming. There will be no more suffering.