How to open illusory walls with messages in front of it?

If there is actually an illusory wall, it will take precedence over reading the message when you hit the interact button. Many of these "illusory wall" messages are in fact fake and attempts at trolling. So, if you find an illusory wall message, try getting close and interacting. If it doesn't work, then the message was a lie.

TLDR: It's a Farce!

Online players know that you cannot access the wall while there is a message there, so they can actually hide the fact that there is no wall, instead causing frustrated players to strafe the wall while mashing the button to no avail.

However: if there is actually a wall there, the only way to access it is to go offline, so that you won't be able to see the messages.

EDIT As @Yuki has explained, if you cannot open a wall due to a message being there, it is an attempt to trick you, because there is no illusionary wall there. Instead, if a message is in the way, the wall will be opened first, then the message will be able to be read.