People have been buying historical manuscripts for years and there is no reason why this trend should stop. The discovery of many of these papers is a long and arduous process that takes a great amount of resources to uncover. Putting them on the open market would compensate those for their work.
With digitalising technology widely available in libraries and academic institutions such as universities, then it is not necessary for scholars to have the authentic text to hand. They can also be viewed in this format in a public museum. Therefore, it is perfectly reasonable for private individuals to purchase historical manuscripts.
Historical manuscripts and documents need to remain in the public domain realm. This means they remain not-for-profit manuscripts the public may read for free. These historic manuscripts and documents are part of the nation's history and as such, setting them up to sell and to make profits only disenfranchises those who cannot afford to read what is their birthright.
Historical documents and manuscripts are the common shared history we as humans share. We should not purchase historical manuscripts as no one person should have ownership to something that is part of our shared history. Ownership of documents of a historical significance may keep hidden secrets and answers for a great many thing. We as humans have a right to know our true history. Copies of manuscripts can be bought, sold, lent, etc but the actual manuscripts should be available for all and protected by public organizations, committees, libraries, museums.