Nothing wrong with a thought-terminating idea. Some affirmations are useful if they terminate self-destructive or nonproductive thinking. Depends on one's goals, I suppose. If you're thought-terminating because the opposing or conflicting or disruptive idea is something you can't reason yourself out of, then it's premature thought-termination and intellectually lazy. If however you're stuck in some pattern of self-destructive thoughts, terminating them as soon as they crop up is beneficial for the psyche.