There is absolutely such a thing as a bad customer, a customer whose loyalty you do not want. Consider that, in order to keep me employed at the call center, the telcom that I support not only has to pay me my pittance per hour, but also enough to the center to cover supervisors, equipment, training, power consumption, etc. Thus, even if someone is religiously paying their bill every month, we could still be effectively losing money on them if they're calling to complain or dispute their bill on a regular basis - to say nothing of the credits they're doubtlessly wringing out of us. If our parent company is losing money to keep you every month, "I've been a loyal customer for years" is not exactly a point in your favour.
My employer does not permit me to say this.
When it comes to my comics and my commissioned art, however, I'm a corporation of one. If interacting with someone is a waste of my time and energy, I will not hestitate to block, ban, or otherwise clip that person out of my life.
Now, don't get me wrong: I try to be accommodating to my commissioners and receptive to reader criticism about Leftover Soup. If someone emails me to complain about how my story handles a particular sensitive subject, I may not necessarily change the comic to accommodate them, but I try to listen and learn, especially if the person criticizing me happens to have relevant experience.
If someone is coming at me with some entitled BS, though - and make no mistake, I get plenty of it - I will not hesitate to remind them that my comic is provided for free and that they are free not to read it. It's quite satisfying, I highly recommend it.