If in almost all cases the warnings are sufficient are you telling me that no child ever repeats bad behaviour?
This is the question: is the price of removal (disruption, perceived harshness, fear of teacher unpopularity) worth the benefit, that is not just stopping current behaviour but deterring future behaviour.
Raven says it is, often. I agree. Evil agrees. You also agree.
But the post-benefit will differ child by child and class by class; and discerning between children will also have a cost in terms of perceived unfairness
These are the judgements teachers must make; and I don't envy you.