Messages Crashes on Mac Upon Startup
Usually I activate the Guest account and use that to test issues like you're describing.

If you try with the Guest account and you're successful, it is an indicator that you've got permission problems with your files.

Unfortunately, Apple's Disk Utility doesn't fix users' files. I've generally found it is quickest to go into the terminal.app and look for permissions that seem out of the ordinary. For example, Application Support folder on my MBP is rwx------

You can view yours by opening Terminal, using cd Library to get into the right folder, then ls -lh to view the folders including Application Support.

If those permissions are different, we can show you how to change them.