It's very well plausible that some people have free will, but others don't. Some people could have incredible stressed attention spans such that they can't think clearly, and others could be more stress free. Some people could be spontaneously relaxed to come up with unpredictable ideas, and other people could be less spontaneous.
Rather than ask whether or not free will exists, why must everyone have the same amount of stress and spontaneity in their attention spans such that they must be treated the same way?
I ask this since as a driver, one thing I've often noticed is my passengers rarely seem to have free will as they like to be lead on in conversation just like they're lead on the road, or maybe that's just part of the job of customer service. Literally, customers relinquish their free will on purpose because they want to be served. They want the service provider to exercise free will for them...
...so maybe there's a second level to the question as well. Perhaps free will is something we can turn on and off. Perhaps the mind has multiple levels to itself such that it isn't simply that people have free will or not, but that people... choose whether or not to choose. Perhaps rejection of free will is a decision of choosing not to choose and not wanting to have to choose to choose.
Of course, there's another matter at hand as to whether some should have to choose to choose while others should be permitted to not have to choose so others can choose for them. Rejecting free will could suggest that people shouldn't have to choose.