It may have once been only a chumra but nowadays with all the consumerism, hedonism, freedoms, sweeping levels of immorality in much of the western world over the last 30 years which is getting worse every year,
Nowadays it may be a chiyuv to seperate as the many of the dangers of influence to the secular world involve serious risks of Issurei dOrayta
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.