Yaatri, truth be told, if someone is going to enter the EU via boat, whether they take the boat first to an island a couple of miles (or less) from the Turkish coast, and then another vs. just taking a longer one is immaterial. In any case the limited visa (entry permit) that the Greeks would give Turks for visiting the islands would have caveats with it that would not allow someone holding such a permit to overstay, or to claim any sort of asylum..............they had it in the past and there were no such problems, in any case most of the illegal immigration such as that which you speak of is THIRD PARTY nationals going from Turkey to Greece (and the EU) and such travel permits would obviously not apply to them.