- Proving $~$P \neq NP$~$ is harder if true than proving $~$P=NP$~$ if true.
- After 50 years we haven't found any efficient algorithm for $~$NP$~$-complete problems.
- The polynomial hierarchy is compared to the arithmetical hierarchy, and the analogy implies $~$P \neq NP$~$ ]
If $~$P \neq NP,$~$ then there are results showing that lower bounds in complexity are inherently harder to prove in a [natural_proof technical yet natural sense]. In other words, if $~$P \neq NP$~$ then proving $~$P \neq NP$~$ is hard.
The opposite proposition for $~$P=NP$~$ is also expected to be true. That is, it would make sense that if $~$P=NP,$~$ then it should be easier to prove, since we could build far more efficient [ theorem provers].
We have been trying to get a fast algorithm for [ $~$NP$~$-complete] problems since the 70s, without success. And take into account that "we" does not only comprise a minor group of theoretical computer scientists, but a whole industry trying to get faster algorithms for commercial purposes.
One could also argue more weakly that if $~$P=NP$~$, then evolution could have made use of this advantage to sped up its search process, or create more efficient minds to solve $~$NP$~$-complete problems at thoughtspeed.
The arithmetical hierarchy argument
Some authors have drawn an analogy between the [ polynomial hierarchy] and the arithmetical hierarchy.
There are results showing that the [ arithmetical hierarchy is strict], and if the analogy holds then we would have that the polynomial hierarchy is strict as well, [collapseofthepolynomialhierarchy which automatically implies $~$P \neq NP$~$].