I reckon Thatcher was mostly hated for her policies. As were Cameron (cuts to provision for disabled children whilst having claimed the max himself), Johnson (COVID parties, lies, Brexit), May (hostile environment, citizens of nowhere, Brexit).
Maybe. But that’s not the point. Labour supporters are just as judgmental as anyone else about the looks and personal presentation of politicians. Objecting to, say, Thatcher’s policies but deriding her background or face, hair and voice is still to deride her.
A good example of the right’s pettiness was John Prescott. A terrible, useless, incompetent man in senior roles in several Labour governments but kept there as a sop to the Labour left (until caught with his pants down). But derided by the right for talking and acting like a rough northerner. The first criticism is fair, the second is snobby.
The point being that Labour and Tories - and everyone else - does judge on looks, accent and all the other superficial stuff. There’s nothing less convincing than a Labour supporter saying they judge only on merit (or a Tory saying the same).