Andrew Charlton and Joseph Stiglitz make a strong argument against preferential trade agreements on the basis of adjustment costs:

There is a high cost to the roundabout approach. For to the extent that there is temporary trade diversion, some industries are being temporarily encouraged, only to be later discouraged. Adjustment costs are typically high in developing countries; there may be significant costs of entry and exit, and with a scarcity of capital, the burden on developing countries may be particularly large. [Fair Trade For All: How Trade Can Promote Development, p.164]

Another arrow in the anti-PTA quiver.