There is some discussion as to the scope of our discussion of this Open Letter. We can comment on this document as researchers and/or as normal citizens.
On the one hand we have many scientists within our membership, who tend to focus rather strongly on science policy aspects. On the other hand, we also have social scientists within our membership with specific competence to deal with economic and social policy. Nevertheless I think we can all have an opinion on how economic and social policy affect us as citizens and affect our research lives.
The Scenario Heading "Schengen, migration & security" does not seem to be a particularly "scientific" issue. Nevertheless as Chair of MCAA, I continually get comments on the need of researchers of many non-EU nationalities based in the UK to get visas to enter the Schengen zone and blaming this on the EU. I remind them that the UK refused (i) to become part of the Schengen zone and (ii) to take part in the EU Scientific Visa programme. This limits researcher mobility (attending conferences or even MCAA meetings) and visa applications are costly and take some time to prepare. If MCAA were to hold a General Assembly in the UK, as MCAA Chair, I would have to sign a very large number of letters to support visa applications by non-EU citizens. Some would simply avoid the hassle by choosing not to travel. This example relates very clearly the reluctance of some UK citizens to surrender national competence for immigration policy that was given such prominence by the Brexit vote and how it affects some MCAA members. Nevertheless those of us living in the Schengen zone continue to enjoy the freedom given to us by a "borderless" Europe.