It can be tough for a man to change his mind once he speaks. But not his thoughts. But isn't a journal a place for thoughts? A journal should be the only place a man can state something only to change his mind later.
But look at the Mark Twain journals. He poured his heart out (to the shock of readers) and it's cast him in a different light. Like we never knew the real Mark Twain. It's assumed that the things he wrote he believed for all time. He hasn't given the opportunity for growth, fleeting feelings, etc.
So journals are, in fact, not a refuge for moments of weakness. They are as permanent as speech. Actually more so. They last forever.
A man can expect to be judged by his thoughts in written form as if they spoke his true belief for all eternity.