Linking another post having a similar kind of discussion. Any justifications for these rules?
On a side note, “चतुर्थ गुणस्थान में शुद्धोपयोग” is a very sensitive topic being the first step of मोक्षमार्ग and directly related to the सुख-दुःख (प्रयोजनभूत).
(Let’s assume, for a minute, it’s a never-ending debate (happening since last +50 years) and we are still in संशय in providing a concrete logic). There is a little / no harm in accepting - “चतुर्थ गुणस्थान में शुद्धोपयोग संभव हैं” but there’s a huge loss in not accepting it. Let’s do a simple Math:
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मिथ्यादृष्टि (who accepts the fact & it’s not true).
The person will try to attain आत्मानुभव being in अव्रती दशा but as we are assuming it’s not true, s/he will not be able to achieve anything… परंतु यह प्रवृति शुभोपयोग रूप होने से 12th स्वर्ग पर्यन्त पद को प्राप्त कर सकता हैं। कार्य सिद्धि तो नहीं हुई परन्तु कुछ बिगाड़ नहीं हैं। -
मिथ्यादृष्टि (who don’t accept the fact and it’s true).
Not believing the fact will not create enough motivation to even think in the direction to attain आत्मानुभव / शुद्धोपयोग / आत्मलीनता / you name it - … सो मोक्षमार्ग दुर्लभ हो जाने से बड़ा बिगाड़ हैं।
I’m not trying to be biased here but Pt. Todarmalji has a really nice contribution in describing the different state of मिथ्या thoughts on a very practical level. We should read his writings (especially रहस्य पूर्ण चिट्ठी) at least once keeping aside our previous beliefs.
Really great to see we have such an awesome place to discuss important stuff (प्रयोजनभूत तत्त्व) without being available in-person, quickly and also not bound to time. Centuries back, the pain for not having such luxury is clearly visible below 
IMG: रहस्य पूर्ण चिट्ठी (last page).