Kerry is an irish jew. his parents became catholic to blend in with society. to prevent discrimination against them. his parents didn't bank on the fact he'd destroy his good name and lie as he has.
It looks more like he had a Jewish grandfather who took an Irish name when he came here.
I can't address his motivation but conversion to Catholicism was not the road to social advancement at the end of the 19th century.
See: http://users.cwnet.com/bwj/kerryirish.htm
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