>Immigration is probably the most important issue of our time. If we have a BI, we can't have immigration in any form remotely resembling what we have today, let alone some ideal situation where we have drastically more immigration. It's as simple as that. The cost of a BI (and the welfare state in general, really) is that millions of people are stuck in Haiti, India, Afghanistan and other desperately poor locales.

No. There are countries that have comprehensive social security and have immigration resembling what we have today - e.g. these countries have immigration that they already have.