Since the whole Torah is equally sacred, with no part more significant then the next, then why are people allowed to sit generally for Torah reading yet we must stand up for the Ten Commandments?
Rambam (responsa 263) opposes standing for the reading of the Ten Commandments for the reason you mention. Rav Ovadia Yosef (Shu”t Y’chave Daat 1,29) accepts this opinion. The Ashkenazi custom, however, is to stand for the reading of the Ten Commandments. This custom is explained by distinguishing between standing for the reading and the reading itself. The danger that we might mislead someone into thinking that only the Ten Commandment were G-d-given would be present only if we were to read the Ten Commandments and not the rest of the Torah. Reading all of the Torah but standing for the Ten Commandments highlights the fact that the giving of the Ten Commandments was accompanied by an encounter on a national level with the Divine Presence. (Tzitz Eliezer 14, 1). Moreover Ashkenazim stand also for Moshe’s song at the Red Sea, minimizing the potential for mistakenly thinking that only the Ten Commandment were G-d-given.