Loss of sovereignty as it pertains to 'migrant quotas'. A country should be able to say - 'no, we have decided to not receive these migrants. These people need to go from where they came'.
Someone will have to provide links on whether migrant quotas were part of the original agreement in the formation of the EU. So if Britain decides its more important to retain their ability to make this decision vs. remaining in the EU, that's a decision Britain can make. And they did.
The African Union/OPEC (probably the only actual authority with any economic leverage in the ME) should designate areas where refuges can be returned.
Morality aside, might/power defines reality in this world. The reality is that the US stirred the pot in the ME, and the EU suffers because of it. In the absence of war crime charges/damages brought before the ITC, this is the only recourse that is within Britain's best interest, based on the election they held.