I guess you didn't read his own words where he criticized SS as being "an instrument for the compulsory redistribution of income...."
Opting in means he had a choice. It means there's a disconnect between his words and his actions. Hypocrisy.
I think you're confused.....
FACT 1.......Koch is the one that criticized SS
FACT 2.......Koch is not one opting into SS at the time
FACT 3.......Mr. Kayek is the person that 'opted' into the system
FACT 4.......Mr. Kayek did not criticize SS....
The only disconnect is between your reading and comprehension skills.....