Final answer:
The line challenged traditional gender roles and expectations and promoted equality and shared values. It was a radical idea at the time and continues to be a radical idea today.
Step-by-step explanation:
The line, "their conduct should be founded on the same principles and have the same aim" expressed a radical idea at the time because it challenged traditional gender roles and expectations. It promoted the idea of equality and shared values, which was not a common belief during that period. This idea of gender equality was revolutionary in advocating for women's rights.
Furthermore, this idea is still considered radical today because gender inequality continues to persist in many societies. The concept that men and women should be treated equally and have the same opportunities is still not fully accepted by everyone.