Let me summarise a justification from Grace7x77 of his view. You have to label every word in scripture, legalistic or grace filled. If it is legalistic or old covenant, you ignore it, if it is grace filled, you accept it.
The problem with this approach is called self fulfilling prophecy. If you take any beliefs, and split them into two groups, acceptable or rejected, you are creating your own belief system. Surprisingly everything you select agrees with your position because you have already pre-selected it. This is called selection bias and it proves nothing.
We have shown Jesus's words, like the Lords prayer is for believers to follow. But the extreme grace group say no.
Why is it for believers? Because Jesus is teaching basic spiritual and emotional realities. These are even obvious outside of faith. What matters above all else is your heart, the core of who you are, how you feel and react, not just how you appear.
This is truth and life. Yet extreme grace will say this is legalism. Now the argument goes this is a lie. Not because it is not true, but because it creates the impression they are wrong. All that is cared about is what is of grace. The rest is just given by the wrong spirit, and evil.
Now I have met this thinking before, in Islam. If you quote the statement of the Koran to show some real life realities, you are then satan, because if it contradicts their view of Islam it must be evil, even if it comes from the Koran.
Now I know you will not accept this truth, because that is the strength of the emotional position. It is destroying the ability to see other points of view which might change your perspective, because perspectives are labeled good and evil, rather than just being perspectives, some of which are helpful and some not so, but you only know which to take once you look at each one and apply your understanding in the Lord. Truth does not fear perspectives, it overcomes them, or shows which are are value. I wonder how many follow the truth, Jesus, and can walk in this reality.