Always, please cite where Rashba bans secular knowledge. Both Rabbenu Bachya and the Gra (on the third perek in Pirkei Avot) say that one cannot be called a sage unless one knows the secular fields. Rambam, at the beginning of the Guide, says that it is a prerequisite to Torah knowledge.
BTW, another Twersky, Rabbi Dr. Aaron Twersky, was the Dean of Hofstra Law School. Rav Hutner encouraged his talmidim to pursue advanced secular studies. Rav Aharon Soloveichik had a doctorate in law from NYU. Rav Prof. (Emeritus) Israel Kirzner is a well-known economist. Interestingly, his teacher in economics was Ludwig von mIses, who was an anti-religious Jew.