comment on the statement

"all elements having high ionization energies also have high electron affinities".

The statement "all elements having high ionizations energies also have high electron affinities" is not correct. For example: noble gases having highest ionisation energies have electron affinity close to zero. 
The electron affinity of group 16 and group 17 is large because gaining electron/s gives these electrons a noble gas configuration. The ionisation energies of these elements is also high.