Yes arguments 3 and 5 could well be applicable to other recently joined nations. But far from shooting down those arguments, the benefit of hindsight (which in the case of these two factors also had the benefit of foresight) is a very good reason to prevent such mistakes happening again.
One of the biggest reasons that Europe should be very wary of Turkish membership is the Schengen agreement. New members of the EU have no facility to opt out of that agreement in the way that the UK and Ireland have. This means that Turkey's external borders will effectively be mainland Europe's external borders. As well as having borders with Bulgaria and Greece, Turkey has borders with Azerbaijan, Georgia, Iran, Iraq, and Syria. Anybody fancy the idea that people crossing into Turkey from any of those nations will have free passage to Calais?
The EU is in a desperate state. The single currency is a mess; many of the PIIGS nations have economies which are teetering on the brink of extinction (witness yesterday's stock market crashes caused by continued uncertainty in Greece); most of the member nations have stagnating economies; deflation is a real problem; the "democratic gap" becomes ever wider as the bloc assumes more powers; waste is rife; corruption is endemic and the budget has not been signed off for almost two decades. The last thing it needs is further expansion which will almost certainly exacerbate those problems.