There’s something so definitive about firing or breaking up with somebody. If you do it, you must be 100% okay with never receiving anything from them ever again. You will never get another hour of work from an employee you fire. You may never see your ex again after breaking up with them, let alone become friends with them. These are extreme measures to take, and one must be willing to face the consequences of cutting someone out of their life, whether it be through work or otherwise. 

If a relationship is bad enough, you won’t care too much if you’ll never see them again. Likewise, if an employee is more hassle than they’re worth, it’s definitely worth the inconvenience of firing them and hiring someone better. You can’t go back to the way your relationship was before cutting ties, so don’t try to crawl back to someone you let go.