If you got accepted a job offer, and within 2 weeks got a job offer for more money, and at your dream company, would you feel obligated to stay with your initial decision?
If you made the rational (but arguably unethical choice), do you think your reputation should be tarnished, and future employers think hard before extending an offer?
I know it's not the exact situation as the OP, but situations are rarely so straight forward, and often have nuances that we aren't aware of.
To the OP, at the very least, you probably dodged a bullet. So blessing in disguise.