I agree - in many cases a surrogate key is better than a natural key. However there is a problem when people start creating surrogate keys by default and stop

I agree - in many cases a surrogate key is better than a natural key. However there is a problem when people start creating surrogate keys by default and stop thinking about the natural candidate key at all, nevermind not putting on the appropriate constraints. Especially in the case where the natural key values are within your control. Also not using them for the key ( and FK ) can create the need for additional joins just to go from surrogate to natural key value.