One ought to avoid (a) being dogmatically sceptic (e.g. in a neo-Kantian postmodern fashion) and (b) using 'scepticism' in service of dogmatism (e.g. doubting the fact of evolution). One may even say dogmatism and scepticism, especially at their extreme ends, form a unity of opposites.
Scepticism may be sometimes correct, but only situationally so. Leftists should not hold scepticism as an article of faith.
BTW, have you read Don DeLillo's _White Noise_? The novel implies that extreme scepticism is in fact anchored by and in turn gives support to extreme credulousness (and that both are nurtured by our media-saturated lives). Then, since the novel has no alternative framework to offer, it ends up dismissing its own scepticism about scepticism. It's a futile irony about the futility of irony, which in the end merges into the white noise of mass culture & commodity fetishism that it appears to criticize.
Yoshie