Just to note: some time ago, in addition to those you mentioned, another vegan EA Forum contributor posted briefly about his '3 doubts on veganism', which is worth reading in full. His concerns were:

• Veganism is too maximalist.
  • The official definition of veganism by its coiners is extremely ambitious. It explicitly requires one to do their best to avoid harming animals in all circumstances in order to be considered vegan.
  • He devolops this point by implicitly invoking the Islamic concept of makruh (discouraged) —stuff neither mubah (permitted) nor haram (forbidden). Smoking is like this; it's heavily discouraged, but you don't put your soul in danger of Hell by doing it.
• Veganism has no room for sinners.
  • Islam forbids drinking alcohol, yet some Muslims drink. Veganism and a vegan diet aren't usually thought to work this way.
  • He notes that Islam succeeded in reducing alcohol consumption to the lowest levels in the world without excommunicating all alcohol-drinking members.
• Veganism is too behavior-focused.
  • In theory, veganism is avoiding "certain actions because of certain beliefs about animal ethics. But in practice, the behavioral part overshadows the belief part."

Just to note, Garett Jones too defends drastically increasing skilled immigration. He specifically opposes open immigration, especially to countries that are at the cutting edge of modernity.

If you are curious about how they differ, Caplan and Jones recently debated immigration here.