Lets face the reality: Most people just don't care. They are not going to feel bad or good, they just know that they did something they consider fast and cheap. Very few people are going to feel bad.
I would, mostly because I have an idea what goes into their food, and I know you are getting what you pay for: there are better options.
But I also have an idea of what the effect of a global race to the bottom from a company like Yum! Brands results in. They own 58,000 restaurants, a training company, a marketing insights company, and a delivery company. Supporting a global conglomerate to supply "cheap" non healthy addictive food should make anyone take pause. They also drive out other options, and feed into the system where we do not have time or energy to make our own food. Fast food at this scale is a pretty nasty with consequences beyond the price at the till.