I'm feeling very guilty because this is the 550th anniversary of the Battle of Wakefield, fought on December 30, 1460, and I haven't prepared a proper post. All I can really do today, then, is ramble a bit.
My own belief is that Henry VI--isolated from his supporters and probably fragile mentally--was bullied into accepting the Act of Accord under which it was agreed that Richard, Duke of York, would reign after Henry's death, thereby disinheriting his own son. The chronicler Gregory writes that after York arrived at Westminster, "he kepte Kynge Harry there by fors and strengythe, tylle at the laste the kynge for fere of dethe grauntyd hym [t]e crowne, for a man that hathe by lytylle wytte wylle sone be a feryd of dethe, and yet I truste and bee-leve there was no man that wolde doo hym bodely harme." The Crowland Chronicler tells of York compelling Henry "to remove to the queen's apartments," while Whethamstede writes that York "went to the principal chamber of the palace (the king being in the queen's apartments), smashed the locks and threw open the doors, in a regal rather than a ducal manner." If such (literally) strong-arm tactics were being employed publicly, what type of pressure might have been applied to the king in private?
Once Henry VI entered into the Act of Accord, his supporters could hardly have believed that the future boded well for him. York and his ally Richard Neville, the Earl of Warwick, had shown no hesitation in ridding themselves of their political enemies at the first battle of St. Albans and at Northampton. The Duke of York was older than Henry VI and faced the prospect that if nature were allowed to take its course, the king might outlive him, thereby cheating him of the crown. Under these circumstances, I think it highly likely that Henry VI's days were numbered once he agreed to make York his heir. (If this was the period during which Henry VI went to Westminster to search out his final resting place, he may have thought so too.) Some convenient accident could have been arranged to befall the king. Even if he were persuaded to abdicate instead of waiting for death to claim him, his prospects as an ex-king would have seemed bleak, given the examples of Edward II and Richard II.
Henry VI's queen and his son--who under the Act of Accord had been left with nothing of his patrimony as Prince of Wales, though it may be that it was intended that the Duchy of Lancaster would be allowed to pass to him upon his father's death --had equal cause to worry about the future. Gregory tells of the "counterfeit tokens" purporting to be from the king that were sent to Margaret (then in Wales) in an attempt to lure her to London; it seems unlikely that the Duke of York was planning a banquet in her honor. Already the Yorkists had circulated rumors about the legitimacy of her son: could York had been planning to start formal proceedings declaring Edward of Lancaster to be a bastard? Or might York have intended to attack the validity of Margaret's marriage to Henry VI? Perhaps York was planning a simpler, more brutal solution. The older he grew, the more of a threat Edward of Lancaster would pose to York and his progeny, even if he were to be officially declared a bastard. Had Margaret of Anjou been foolish enough to let him fall into Yorkist hands, the boy might well have become the first Prince in the Tower, disappearing like the sons of Edward IV did during Richard III's reign. Or perhaps he might have been imprisoned and eventually executed, as young Edward, Earl of Warwick, would be during Henry VII's reign.
All of this is speculation, of course. But such thoughts likely occurred to Margaret of Anjou and her followers as they raised troops to oppose the Duke of York. Under those circumstances, the duke and those who fought alongside him could hardly expect mercy from the Lancastrians, and it's no surprise that they didn't receive it at Wakefield.