It's because you normally expect a certain level of professionalism when it comes to business. Regardless of who is in the wrong. Imagine if a police officer that caught you speeding started cursing you out for almost hitting their patrol car. Maybe it's justified but that doesn't mean they should do it.
Also, who are you to call the uploaders disgusting when you're reading their uploads? If you're on this website you're just as guilty as the people you complain about.
Maybe the correct metaphor is (considering the author is not a law officer, and considering that this is unauthorized publishing of commercial webtoon)
You find someone stealing in your store. What would you do?
a. Tell the person nicely to give it back
b. Call the police
c. Chase the person out of your store
I'd pick b and c
the fact you all are calling the author rude is really not right because if the author is actually really chill and pretty nice haha but the audacity to still upload the chapters is so disgusting