I think an awareness of our own confirmation bias is about the best we can bring to any historical investigation - whether we're inwardly rooting for the slaves in the Third Servile War, or experiencing a general "ugh" feeling when a writer is obviously espousing a set of values with which we disagree.Yes. Reading critically while your inner voice is cheering and laying out dessert is very hard. For me it’s a toss up between that and reading critically when a book is loathsome and howlingly wrong in major ways but also has some crucial data and genuinely insightful analysis.
I recently re-read A History of Venice by John Julius Norwich - he's been widely criticized by historians as bringing nothing new to the table, and regurgitating tired old tropes and theories which were debunked decades ago. He was a staunch pro-establishment figure - opinionated, aristocratic, conservative, a monarchist etc. I disagree with pretty much every view he held.
But damn, the man could write. Venice is a rollercoaster which still gripped me thirty years after I first read it.
And that's another problem. If a history book, however impartial and evidentiary in its contents, is boring then it can be hard to slog through it, and I get glazed eyes and start to nod off.