I am not so sure it has infected the left, it is portrayed as having infected the left, It has been the case since Labour councils were portrayed as giving huge amounts of money to causes such as one legged lesbians against the bomb and other such monikers,
I genuinely can not remember ever one time when I discussed with friends who are left wing issues such as trans rights, taking the knee, or any other of these culture war issues. I have discussed with them with a friend of mine who holds very right wing views and is against people taking the knee, is against trans rights and all the other issues that the culture wars have produced. I do believe the culture war issues are created by the right wing to cause division where there was no division before. America does it with the abortion issue, where it is seen as a right wing cause to be pro-life, no doubt that issue will surface here at some point promoted by RW politicians in order to create further division.
The aim of using these issues is to divide the working class, because it suits the Capitalist class to keep the working class divided. Whilst the working class are arguing over whether taking the knee is something that began with Martin Luther King or its in support of what my RW mate says are "Marxists intent on destroying civilisation" its the capitalist class who laugh their bolloxs off and steal the countries treasure.
I mean since when has been advocating for antiracism been a bad thing, because it isn't, for the simple reason most of the victims of racism have more in common with the working class kids than they do the exploitative capitalist class as they are working class themselves. My next door neighbours are a family of Nigerian heritage, they are hard working, he works on the rigs, she works in an office and I have far more in common with them than i do with say Jacob Rees Mogg and other RW fruitcakes. Me and him talk about the football, his wife is good with my mam, the kids are polite just like kids from council estates are supposed to be towards their elders. If the Capitalist class and the RW fruitcakes get there way, i should be looking down on my neighbours as they not my equals, i am their better. Which is of course fucking nonsense.
I do think Starmer has a liberal vision for the UK, Corbyn too in some respects, because the labour party moved rightwards under Blair towards this mythical centre ground. To me being on that centrist ground means you accept that capitalism will exploit the working class and you will try and use it to distribute wealth more equally, where as i believe that is the wrong place to start and we should be subduing capitalism and getting rid of its excesses and following a state capitalist/nationalisation model where the people have more democratic say in their lives and people are put before profit.
The Labour party has to find a message that resonates with the working class, you are 100% correct in that it is not a message that involves calling Bernard from Bacup, Miss because he wears a dress, it should be about the things that matter like good housing, decent schools, a well funded health service, the stuff that means our kids get a good start in life so they can make the best of their abilities. it should never be about equality of outcome but of equality of opportunity.