No, since the claim “veganism does cause intellectual deficiencies” is still wrong, because veganism doesn’t cause this, a lack of supplementation does. And most vegans supplement adequately. So saying that veganism “per default” causes this would be dishonest, because it implies that not properly supplementing is the default/intrinsic to veganism, which is not the case.

It’s like saying “drinking alcohol kills you” just because you have to be mindful of limiting your consumption and it can kill you if you don’t. An extreme statement that contains a kernel of truth, but is simply not correct.