Writing for Campaignlive.co.uk ahead of the broadcaster’s upfronts at the Palladium tonight (Thursday), Williams explained that TV should aim to "cut through the truthiness – arguments or assertions without regard to evidence".
He contrasted the "trusted and impartial" world of TV with online, where he said there is a litany of problems such as "ad-blockers, view-ability and non-human traffic".
His comments about "truthiness" follow the campaigns for Brexit and the US election this year, which featured many claims that turned out to be inaccurate.
Williams wrote: "TV is a force for good and has huge power to do positive things for society." Broadcasters also use it to launch appeals and campaigns "and this type of initiative is funded to a great extent by advertising".
He cited Channel 4 for championing disability with Maltesers and ITV’s Team GB work with The National Lottery.