I think they are warning tourists rather than those of us who know our Shakespeare. It's a 'must go to' venue for many. My daughter, living in London, attends the Globe very regularly, usually as a groundling. A groundling, for those not familiar with the term, is someone who pays to stand in the pit. She saw Titus Andronicus there and got covered in theatre blood. She knows to wear old clothes or have a waterproof covering. On that occasion 3 people fainted. The highest count, she believes, for Titus is 14 fainting. That creates problems for the staff who have to remove said person or at least make them comfortable. For anyone who has attended as a groundling you will know how space is limited. On her last visit, an American who had paid to be a groundling, argued with the attendant to show him where his spot to stand was and had great difficulty understanding it was a free for all. Regulars always get the best spot because they queue, English fashion, to be first admitted and then run. I think the warning is a case of 'If you can't stand the blood, stay out of the Globe'.