That they can lie is disputed. Lieing is forbiddin in Islam, but some people use Mohammed's attack in violation of the Treaty of Hudaybiyah as justification. Problem is, the other signee, the Quaraish, had already broken the non-belligerence treaty by aligning itself with another tribe and attacking one of Mohammed's allies. It was right for Stalin to eventually invade Germany despite the non-aggression pact with Hitler, right? Why? Hitler broke it first.
So of course those who want to lie will use this for their justification, hoping people don't know the whole story. Likewise, justification to lie to achieve an end can be easily supported by a quick Bible reading.