Opinions should be formed with great caution, and changed with greater.

Two different dangers are being named, and most people only guard against one. Forming views too quickly leaves you holding positions you never examined. Changing them too easily leaves you with nothing that holds, blown about by whoever spoke last or most confidently. The discipline is slowness at both ends, so that a change of mind is a considered event rather than a mood.

When a new argument moves you, wait before you adopt it. Write down what would have to be true for the old view to still be right, and check that honestly. If it still fails after a week, change, and say so plainly.