During his keynote speech to delegates at PRWeek's Global Festival of PR, Shield described the BBC as "a national treasure as well as a national punchbag".
He went on to claim that while a lot of politicians and newspapers held certain views about the BBC, "the public are often in a different place".
When it comes to dealing with critics of the BBC, Shield said: "I don’t believe in the squabble approach to comms but I think those people that make allegations about the BBC that I think are wrong, then we will push back and we will call people out on that."
He added: "I think people expect you to defend yourself, but comms is much more than having a good rebuttal machine, it’s fundamentally about actually setting out why you’re there, why you’re valued and why you want to do a good thing."
The international reach of the BBC, particularly through the World Service, is very important, according to Shield. "I’ve yet to find somebody who will really have a go at the World Service, it’s still hugely treasured," he remarked.
"The government has put more money into funding global services and I think the BBC is very important in projecting soft power and British values," added the comms chief.
"If we are concerned about democracy, if we are concerned about impartiality, if we are concerned about shining a light on repressive regimes wherever they are in the world, if we are concerned about telling the stories about the challenges people face then the World Service is absolutely vital to that," said Shield.
But he also warned that cuts to the funding of the BBC mean the broadcaster would face "some very difficult choices" in the future and "the BBC won’t be able to do everything it currently does."
The broadcaster is currently going through a governmental review of its Royal Charter, a politically charged topic which has led to debate about the corporation's size, operations and aims.