[grey-area]

I really don't think you can fairly characterise this as pure aesthetics - "an eye, but what an eye!". Clearly producing a new home page without knowing a company and with a superficial understanding of their products and requirements is quite a shallow exercise which does not encapsulate the totality of design practice. I'm sure the poster is well aware of that, but that doesn't mean it does not involve thinking about the products and requirements, and only focussing on aesthetics.

This is not design in the holistic sense, but that does not mean it is not a useful short exercise and potentially a useful collection of user feedback for non-designer founders who have neither the time, the money, nor the inclination to hire a designer - perhaps seeing a redesign will prompt them to think further on the designs they have, which probably grew organically with the sites.

In short it is only dangerous if you mistake this sort of exercise for a complete design process. No designers would, and no clients I'd want to work for would either. I think it's an interesting and useful thought experiment, though obviously limited in scope, and the designs so far have had some useful hints for the site concerned - I particularly liked the wave one, which humanised the product and neatly summarised it in one image.

On the Internet it is easy to criticise or run things down. This sort of exercise brings back constructive criticism which is so hard to do well - the sort of thing that starts conversations, not arguments. If you see it as only the start of a process (one of many possible starting points) perhaps it will come to seem less dangerous and more fruitful.