There was discrimination long before Voldemort. Phineas Nigellus frequently uses the term Mudblood. It shows that the prejudice was firmly embedded in magical society centuries before. Various members of the Black family were blasted off the family tree for being either Squibs, marrying Muggle-borns, or championing Muggle-born rights. Perhaps Grindelwald wasn't that bothered about Muggle-borns and was more concerned with ruling over Muggles, but he was foreign and that may not have been as big an issue in Durmstrang. (Although, I tend to think Durmstrang was far more pro pure-blood than Hogwarts, but that's my interpretation)
Until Voldemort came along, there wasn't much discrimination against Muggleborns (I do believe that Grindewald's campaign was to have wizards rule over Muggles, could be wrong though). Hermione isn't discriminated against in school, she is simply bullied.