Turkey would actually be the poorest nation within the EU by gdp per capita, much poorer even than the Baltic and Eastern European states.
They are now becoming more despotic by the week - newspaper offices and tv news agencies are being invaded and gagged by Erdogan and his government, and reporters have only recently been arrested and jailed without charge for writing anti-government articles! Hardly the progressive muslim country that some are trying to convince us they are.
Turkey has air power and a huge land army that they are currently using to bomb the Kurds that are actively fighting ISIS. Do you really think it a good idea to allow accession to the EU of a country that would deal oil with ISIS whilst actively hampering attempts to fight the terrorist organisation? I could also mention that despite this huge army, they are unable to secure their border and control the movement of people within Turkey as they have so far allowed over 130,000 "refugees" to cross into Greece illegally. These are not exactly the actions of a nation that has any intention of either 'westernising' or controlling their border with a neighbouring country and, by default, the EU.
I do hope for a Brexit.