Privacy checkbox disabled by default

Is it possible to have all company accounts to be forced into enabling "Require Log-in to view uploaded files"?

Security by obscurity for possible confidential information should be avoided. 

Is it possible for force a profile or security setting on all company accounts for any employee using this Slack app?

Unfortunately, there is no way to force these security settings to any account. If there are multiple accounts being used in your company you will have to ask each one of them to enable the upload security settings.