Protecting your app starts by protecting your users. There are several HTTP headers you should already be using in your web apps but one usually overlooked is Strict-Transport-Security
This header ensures that the browser will refuse to connect if there is a certificate problem like in an invalid certificate presented by a MIM attack coming from a malware in a user's computer. Without this header the user will be giving away absolutely all "secure" traffic to the attacker. Additionally this header will make sure the browser uses only https protocol which means no insecure/unencrypted/plain text communication happens with the server.
The motivation for not using this header could be to allow mixing insecure content in your pages or to allow using self signed certificates in non production servers. I believe such motivation is dangerous when you consider the risk. Your application will be more secure if you address security in the backend and in the front end, the same way you should do validations in the front end and the backend.