We must also ask ourselves if it is normal within a healthy perspective of faith to aim for a goal in which the only thoughts you have are those you consider that your perception of God would consider to be pure.
You make a good point. It has a subjective component tied to it. But people know what is bad and what is good. Not everything is pure subjectivity. If you're a Catholic/Eastern Orthodox the basic consensus is that human defects are the cause of sin. Anxiety and mental disorders and the psychological aspect in the past (before modern psychology) were resolved with confession, prayer, fasting, and almsgiving. Why? Because if purges evil from us and orientates us towards God.
What you are calling 'good' or 'bad' are not subjective measurements. People know when something is good and when it is bad. When the mind is clouded by evil can they recognize this? Maybe all the more, maybe all the less, they have become blind. God also gives consolations and desolations to individuals, which is God's doing and His determination. God does indeed test us, so keep in mind to gain virtue one must first overcome some sort of evil obstacle in the process.
You overcome evil with Christ and this makes us grow in Holiness and perfection. Yes, you want to disregard evil thoughts and ideas and motives, but you have to realize that that's what they are, 'evil thoughts and ideas'. They aren't abstract nothings, they are 'principalities and powers', absences of virtue, defects, and disorders which need overcome with prayer and fasting and specifically Jesus Christ.