I am not having any issues at this time. I do not mess with permissions and such and in fact I have never really learned to use them except through the folder/file>preferences>permissions tab.
But my question is, if a person messed around and screwed up permissions all over the computer, is there a command that would reset all system permissions to the default state?
There isn't a single command that I'm aware of that will reset permissions that have been altered. Linux allows the user to do both useful and self-destructive things to installations. It's non-discriminatory that way.
Linux will let you create your own warnings if you want it to, for example if you alias the remove command: rm, to: rm -i, it will prompt you each time you use rm to remove a file instead of just removing it wthout further ado.
There isn't such an option for chmod when changing permissions, but it could be scripted.
Recovery from permissions problems due to alterations to file permissions depends on the situation.
If one has been changing permissions in a terminal using bash for example, if they have a .bash_history file configured, the commands that they've used for altering permissions may all be recorded in the .bash_history file. In that case they can all be identified and reversed. Similarly for the root user, if there's a .bash_history configured for root.
Another means to finding files that have been altered is to use the find command with it's time locating options. For example, if you knew that the alterations had been made only in the last week, you could try and find all files that had been altered in the last week using the "-ctime -7", option to the find command which will identify files with permission changes, amongst others.
There are other ways to detect such changes as well which could be written up in scripts to get the information utilising the stat command which shows file alterations.
If the changes to permissions have been made through a file manager, then a record of those changes may depend on the file manager's history logs, if they have any, and I'm not familiar with any that do so thoroughly in relation to permission changes, but my experience with file managers is limited.
There are system level ways to go with this issue which can be done using the audit daemon from the auditd package. It would need to be configured for the purpose of monitoring permissions apart from the numerous other things it can monitor and have logged in a log file. It may however, be a bit like using a jackhammer to hammer a tack.