Then why do you access their computers when they have explicitly said they don't want you to? Even further, you circumvent a system they have put in place to stop you from accessing their property.
They didn't give it to you. They put a wall and said "You cannot pass this wall with adblock turned on". You decided to circumvent it. Because...?
Their "wall" as you describe it is actually just client-side code which runs on _my_ computer, not theirs, so I get to decide how it executes. It would be completely different if the "wall" was on the server side of course (for example, a paywall).
If it's on my computer, it's under my control. Just because it came from their server does not mean it has any rights on my computer at all. They're not entitled to my computer.