Doctors in Bradford, for example, have pointed out that high levels of genetic birth defects in the city owe much to the practice of family interbreeding, common among arranged marriages in the Pakistani community.
And the fact that so many of these marriages involve bringing in husbands or wives from Pakistan, who frequently speak little or no English, has been identified as a major factor in holding back the linguistic development of Pakistani children and hampering their educational achievements.
Now Lord Ahmed of Rotherham has suggested yet another worrying aspect of first-cousin marriage. According to the Muslim peer, it is the fact that so many arranged marriages to first cousins are unhappy that leads some young Pakistani men to fulfil their sexual needs with vulnerable young white girls.
In the light of court cases in which young Asian men have been sentenced for grooming white girls as young as 12 in Derby, Blackburn and Lord Ahmed's home town of Rotherham, this is a controversial claim. But it is also one that demands further examination.
Too often the leaders of Britain's Pakistani community have tried to brush problems under the carpet and condemned as racist those who seek to bring them to light. Lord Ahmed should be commended for his bravery in speaking out.