Debarking/devocalizing wasn't widely practised until the mid 20th-century. As you note, it is an extremely controversial practice and illegal in many countries.

In the past, there wasn't much demand for this sort of operation as a barking dog was a very valuable deterrent against thieves — pets and working dogs were both well-regarded for providing this sort of service. Dogs were not the recipients of specialist veterinary attention en masse until the mid-20th century anyway.

There were some exceptions. Scientists experimenting on dogs might carry out operations to prevent their howling, but they were quite different to today's debarking operations which focus on removing tissue from the vocal cords. In early 19th-century Paris, a scientist named C-P Collard de Martigny cut the vagus nerve of a dog he was starving in order to prevent it crying from hunger and disturbing the neighbourhood. The operation silenced the dog, but only temporarily.

This was the main criticism of debarking procedures made by a 1949 text on veterinary surgery, which noted that although operations to silence dogs had been carried out for some years, their results were often considered disappointing and the effect was generally only temporary. The authors of the book note that euthanasia was generally a much more popular option for owners of pet dogs who barked excessively and that there was considerable opposition to the procedure. Nevertheless, the textbook guided veterinary surgeons in how to perform the operation effectively. By the 1950s and 1960s debarking had become more popular and in 1961 an article in the New Scientist noted that the procedure is 'extensively carried out in the United States'.

The popularisation of debarking relied on the development of small animal veterinary surgery in the 20th century alongside changing modes of dog ownership. There were an increasing numbers of indoor dogs valued primarily for companionship and more owners hesitant to euthanise them for behavioural problems and willing to pay for an effective surgical intervention. There's also something to be said for companion dog ownership as a middle-class suburban phenomenon here; a dog that barks at every hour of the day threatens the peace of the neighbourhood.

Sources

Tom Almeroth-Williams, ‘The Watchdogs of Georgian London: Non-human Agency, Crime Prevention and Control of Urban Space’, The London Journal, 43 (2018).

Susan Jones, Valuing Animals: Veterinarians and Their Patients in Modern America (2003)

Boisseau, Bouillaud, Brichetau, Dezeimeris and Gaultier de Claubry, ‘Bulletin de la Société médicale d'émulation', Archives générales de médecine, 25 (1831), p. 223.

Horace Preston Hoskins and John Victor Lacroix, eds., Canine Surgery: A Text and Reference Work (1949), pp. 201-202.

[Geminus], ‘It seems to me’, New Scientist, 2503 (31 August 1961), p. 549.