You are grasping at a straw. No significant cotton can be grown in any of those places today without serious irrigation systems being employed.
If it cannot be done today, no serious amount of cotton could have been grown in those places back in 1860. The idea that those states represented a massive addition to the propagation of slavery is just false.
As I pointed out in the Wikipedia article on the Crittenden compromise, both sides acknowledged that slavery wasn't going to be significant anywhere in New Mexico or Arizona or Nevada.
According to this source by 1860 the number of slaves in New Mexico was already at least hundreds if not thousands.
The key feature of Crittenden was it reestablished the old Missouri Compromise 36-30 line between slave & free territories.
Democrats liked it, but Republicans opposed expanding slavery beyond states where it was already lawful.
"Raw power"?
Maybe for some, but people like Abe Lincoln also believed slavery was morally wrong and should be opposed where possible.