I've no problem with either side of the pond charging for visas or making people go through checks before they could get one. If countries begin to make it difficult for foreign airline crews to get in and out of their country on a work basis where will it end.
If it all degenerates into tit for tat obstruction we'll all be flying domestic flights for the near future. Governments will have to ensure that they have adequate staff in their immigration departments to process visas in a reasonable time frame.