A principal resposta para essa pergunta está em Harry Potter e a Pedra Filosofal , em uma conversa entre Hagrid e Harry, no capítulo Beco Diagonal :
‘But what does a Ministry of Magic do?’
‘Well, their main job is to keep it from the Muggles that there’s still witches an’ wizards up an’ down the country.’
‘Why?’
‘Why? Blimey, Harry, everyone’d be wantin’ magic solutions to their problems. Nah, we’re best left alone.’
Philosopher's Stone - page 51 - British Hardcover
Editado para adicionar: encontrei algumas informações adicionais sobre este tópico. Em Tales of Beedle the Bard , Alvo Dumbledore segue cada história com seus pensamentos escritos e uma análise de cada história. Depois de The Wizard e o Hopping Pot , Dumbledore oferece os seguintes insights:
The persecution of witches and wizards was gathering pace all over Europe in the early fifteenth century. [SNIP] "Let the Muggles manage without us!" was the cry, as the wizards drew further and further apart from their non-magical brethren, culminating with the institution of the International Statute of Wizarding Secrecy in 1689, when wizardkind voluntarily went underground.
Tales of Beedle the Bard - page 40 to 41 - US Collector's Edition
As the witch-hunts grew ever fiercer, wizarding families began to live double lives, using charms of concealment to protect themselves and their families. By the seventeeth [sic] century, any witch or wizard who chose to fraternise with Muggles became suspect, even an outcast in his or her own community. Among the many insults hurled at pro-Muggle witches and wizards (such fruity epithets as 'Mudwallower,' 'Dunglicker,' and 'Scumsucker' date from this period), was the charge of having weak or inferior magic.
Tales of Beedle the Bard - page 43 to 44 - US Collector's Edition
Influential wizards of the day, such as Brutus Malfoy, editor of Warlock at War, and anti-Muggle periodical, perpetuated the stereotype that a Muggle-lover was about as magical as a Squib. Brutus wrote:
'This we may state with certainty: any wizard who shows fondness for the society of Muggles is of low intelligence, with magic so feeble and pitiful that he can only feel himself superior if surrounded by Muggle pigmen. Nothing is a surer sign of weak magic than a weakness for non-magical company.'
Tales of Beedle the Bard - page 44 to 46 - US Collector's Edition
As anotações de Dumbledore sobre O Feiticeiro e o Hopping Pot fazem um pouco mais de detalhes sobre a perseguição dos bruxos e feiticeiros aos trouxas. Ele menciona que Nick Quase Sem Cabeça foi despojado de sua varinha antes de ser jogado em um calabouço para aguardar a execução e foi incapaz de se iludir fora da situação. Além disso, quanto mais jovem a bruxa ou bruxo, mais correm o risco de serem executados, devido à sua menor capacidade de controlar sua magia (como visto com Ariana Dumbledore e seu subseqüente ataque de três garotos trouxas depois que eles a testemunharam fazendo mágica e Ariana incapaz de reproduzir o truque à demanda dos meninos). Veja a página 41 em Tales of Beedle the Bard para detalhes completos.