A basement creates extra space and value, and avoids the upheaval of moving house permanently. For neighbours there is attendant noise, disruption, the fear of possible structural damage and worry about possible effects on ground water or trees or suchlike.
For the Suburb at large there are additional considerations. The grouping of similar house types and sizes in streets and closes, combined with a very wide variety of dwelling sizes across the Suburb as a whole, was critical to the aspirations of the Suburb founders for a mixed and varied community open to all. The creation of basements affects the balance of that mix and the character of the Suburb.
Supplementary Basement Guidance