Performing in costume

This may need more than one post to discuss, but it is clear that 'serious' performers of medieval music rather look down on anyone who plays in costume. For example in the essay by Benjamin Bagby that I have discussed before, he starts out by characterising the expectations of a modern concert audience in terms of atmosphere, duration, programme notes, etc., as potentially problematic, because it influences performances in ways that have nothing to do with the medieval. I agree that performances can indeed be over-tailored to avoid any risk of audience confusion or alienation, to the detriment of authenticity. But he goes on:

 "This fear of alienation is a slippery slope descending towards the ridiculous, as any ensemble which has tried dressing up in pointy shoes and pretending to be ‘medieval’ can attest."

I should admit a bias here as someone extremely fond of the medieval pointy shoe (and so much more comfortable than the modern high heel that a female performer might otherwise be expected to wear!). But why does he think it so obviously ridiculous and pandering to the audience to dress as they did in the middle ages when performing medieval music? Why, indeed, isn't this 'odd' clothing potentially seen as more alienating  to an audience, more risky, than standard concert dress?

There are at least two issues here, I think. One is that the medieval costume is seen as all part of the 'drums and fun' attitude, which prevents the music from being taken seriously. The other, as hinted at in the quote, is that by wearing a costume, the performer is 'pretending' to be someone they are not, some character from the middle ages; rather than being themselves, playing music from the middle ages. I don't think either is a good reason to suggest the practice is inherently ridiculous.