A sheikh claims that everything is initially halaal until proven haraam.

Answer

In this age, any Tom, Dick and Harry, even every Jane, Janet and Jill believes himself/herself to be a Mujtahid. He/she extracts a Hadith, etc. from books and subjects it to his/her opinion to produce moronic, convoluted fatwas of jahaalat.

It is not permissible to eat anything if one is not aware of its classification. This has more emphasis today when even Muslims cannot be trusted regarding meat and chickens. For the sake of monetary gain they are halaalizing carrion and haraam meat. Furthermore, it has already been proven by deluges of evidence that all commercially killed chickens of these kuffaar killing facilities are haraam. The principle of initial permissibility no longer applies, especially when the chickens have been proven to be haraam carrion.