Heaviside's comment, famously, was "Shall I refuse my dinner because I do not fully understand the process of digestion?"

That's not what he's saying. He's just making an observation that physicists have a tendency to make mistakes with math if it's convenient for them, so it's generally not a good idea to use their proofs when you're wanting something mathematical.

I guess that's more charitable. But to my ears it sounded like a baldly pedantic critique of what is easily one of the greatest theoretical results of the past century.