The Thatcher quote Starmer mentioned
British Political Speeches
She was attacking Labour in her first Speech as Party Leader, Tory Party conference in 1975
What she was attacking (Clay Cross Council and the Shrewsbury Six amongst others), she was very wrong in what she was saying but Starmer was quoting the emboldened bit above out of context, to throw Thatchers words back at the Tories. In isolation, it's hard not to agree with that selective quote. It's easy to disagree with the overall content of that speech but that bit that Starmer used should be a universal truth.
The headlines about Starmer's speech are a bit wonky, "Starmer Praises Thatcher", he was doing nothing of the sort, he just said one thing she said was right
We've got a Tory Government who ignore the rule of law. Thatcher wasn't wrong with the quoted line and so to use Thatchers words against the Tories seems rather apposite and also hard for them to disagree
It's easy to see the headines "Starmer quotes Thatcher" and see why he did it. It will resonate with Tories, it will also upset the Left but the headlines will do their job as most people won't actually listen to the actual quote, just read the headlines
There is absolutely nothing wrong with that line from her speech though (The rest of the speech was utter bollex)