All these characters who are portrayed at any point as being even somewhat sympathetic, are swayed by reason - and , in particular, the reason of the Doctor.
Away from violence, which would lead to war, then armageddon, then invasion and enslavement by the Daleks - Doctor Who's perfected symbol of hatred and devastation.
If their role in the narrative is to be read as analogous to both the causes and effects of mutually assured nuclear destruction, what we have is a story that is not just anti-war and pro-internationalism (via diplomacy and detante) but more so as a vision and embodiment of humanity's ultimate defeat averted by just one thing - reasoning.
In 1971, at another high point of the Cold War, Day of the Daleks is a clarion call that wedo not have to end up amongst the ashes and dust - that we can choose not to by electing to strengthen diplomatic ties simply so as better to understand others who are not necessarily out enemy, though might at first appear to be.
It calls to mind Peter Capaldi's defining speech as the Doctor in The Zygon Inversion, where all that it takes is for us to SIT DOWN AND TALK!