No one wakes up one day designing to throw their ethics out the window. It happens slowly, one slippery slope at a time. It's a series of small decisions that might even seem fine at the time, and before you know it you're designing filtering UI for the Walmart online gun shop.
Take the time for self-reflection every few months. Evaluate the decisions you've made recently.
Are you staying true to who you are? Or are you slowly moving your ethical goal posts a few yards at a time with each raise or stock option award?
Have you veered off course? Correct it.
Is your workplace an unethical hellmouth? Get another one.
Your job is a choice. Please do it right.