The Venn Diagram which shows Americans who support the wall with Mexico and Americans who support Turkish entry into the EU probably doesn't have much overlap.

To your points:

The bill for upgrading Turkey's infrastructure won't be trillions of dollars. The total money available to the EU in the next 7-year financial framework is about 1 trillion dollars. Of that money about 350 billion goes to cohesion. Turkey would get its fair share of these funds if it were to join by the next financial period, but the amount is not likely to exceed 0.1 trillion over 7 years. Right now the EU is paying to the tune of 500 million, which will soon increase to 1 billion.

Having a border with Syria, Iraq and Iran does not increase our problems with these countries. The EU is not a defensive alliance. Turkey is already a NATO country, so if it is attacked by either we have to help anyway.

The Kurdish issue is not more or less intractable than the Basque and Irish issues once were and the issues on the Balkan still are.

The number of votes in the Council is a poor indicator of a country's power in the EU. Compare Italy, the UK and France, who all have the same number. Compared to France, Italy has very little power, and the UK not much more. Turkey will be less poor (it has a far quicker growth than most European countries), nationalist and militarist when it joins.

The immigration of Turks now continues apace under the motto of marriage and family reunion. There is no particular reason why this would dramatically increase. The Turkish people who were collected as guest workers were largely rural and very religious. There is also a citizen class in Turkey which has different customs and will be more open to intercultural marriages.