Stocks can be analyzed by looking at performance of the company, state of the market and so on, and then calculating how much should they be worth, based on expected profit, but if a company lies about the state of its operations, you will get defrauded, even though you used math to calculate "objective" value.
Math doesn't make an idea objective. Objectivity doesn't mean "using logic or math". It means "volitional adherence to reality". It means turning your mind towards reality to identify facts and use them in your evaluations.
The fact that you can be defrauded doesn't mean that facts don't exist, or you don't try to use your best judgment and perform due diligence to ensure that what you think is true actually is true. That's what it means to be objective.