I don't go seeking after Frankie Boyle but I sympathise with the position he's in. Channel 4, like the BBC before them, hire him because he's outrageous and then fire him because he's outrageous. It's as if they're gleefully egging him on to let fly with the barbs but as soon as one of them lands on a group they perceive as "vulnerable" (one of the weasel words of our time) they hastily compose their features to indicate disapproval and ask him to step into the office.
It was the same with Russell Brand during his time on Radio Two. You hire him because he goes a notch further than Jonathan Ross and then fire him because he's gone two notches further. That's the nature of the beast. If you tell somebody that their appeal lies in their outrageousness you must expect them to aspire to outrageousness, which can be quite easily measured by the number of times they cross the line, rather than humour, which is a lot more subjective. And harder.