chip away

[Romel Panzer]

“The truth is that many of their assumptions about the underlying causes of extremism are flawed. Every fresh terrorist attack “chips away” the idea that foreign policy and socio-economic factors are the sole drivers of Islamist extremism, making the Muslim default position more untenable.” I think the meaning of “chips away” in the above is “to lessen the effect”, “to weaken”. And the “Muslim default” here means cause due to Muslims. Please clarify and confirm.

[Tdol]

Chip away- lessen, weaken little by little
Default position- the standard position they use as an argument/defence

[BobK]

(There's a missing 'at' in the original.)

Every fresh terrorist attack chips away at the idea...

Explanation: there is an idea; each attack does not refute it entirely, but weakens it in a small but progressive way - it 'chips away at' it.

b