The need for separation was always important. Dont know if it was a chumrah or halachah or wtvr but hashkafikly speaking even when living with and doing business with non jews there always has to be an understanding that were different (each jew according to his guidelines.)
Its not so simple to talk about on a public forum cuz things can get misunderstood. But, the classic saying was that if we don’t separate ourselves then we’ll get seperated.