There are three major drawbacks to adjusting to GW or just letting it taking its course.

Uncertainty,
The overall climate of the Earth is well suited to man as it is. Any dramatic change is likely to be for the worse.

Expense.
On a global scale it would be cheaper to decrease the effects than deal with them. Conservation now is way cheaper than dealing with drought, storms and displacement.

Conflict,

As disparity and desperation increase war becomes inevitable. Even the US military, not known for its left leanings predicts conflict if the GW trend continues.