I was not contending that cancer prevention was the primary benefit of
introns. Not by any stretch. I believe that introns facilitate the
splicing and introns probably have other functions and benefits.
"If introns really distract mutagens from hitting exons, wouldn't the
likleyhood of a deletion in an intron/exon increase? Wouldn't this
increase the likleyhood of a frame shift?"
Mutagens cause point mutations far more often than frameshifts. Why
would a deletion occur? Mutagens bind and prevent correct reading of the
codon. They do not normally cause deletions to my knowledge.