The rationale around health and mental risks, genetic defects and other consequences are universally accepted. However, one thing looking through Hansard that caught my eye was this line:

However, the way to redress the issue is not to empower the state to ban adults from marrying each other, not least because I do not think such measures would be effective or enforceable.

I whiff a Trojan horse of more Government intervention in people's lives that will go beyond cousin marriages. There is going to be a "but" added after that sentence because Governments never let an opportunity to have more control over your private lives slip from their fingers. It'll be sold on the grounds of ending cousin marriages, a noble goal but won't stop there.