CAMBRIDGE – In the quiet streets around Cambridge station, the memory of Mohammed Algasim lingers not as a statistic but as a cautionary tale of what can happen when the pollution of hateful rhetoric is allowed to seep unchecked into the public square. Almost a year after the 20-year-old Saudi student’s life was ripped away in a single, devastating knife thrust, his father has broken a family’s dignified silence to issue a stark warning: Britain’s reputation as a safe, welcoming destination for international students and tourists is being shredded by a surge in racism and Islamophobia that he believes claimed his son’s life.