"I see. I guess that is one way to think.
Then let me ask you, Emiya Shirou. Do you think you can beat your own Servant?"
"Then let me ask you one more thing. It is a boring question, but do you think you are superior to your Servant?"
"…??"
What's he saying?"
I can't beat Saber, so there's no way I'm superior to her.
For this question, my answer will always be that I am weaker than my Servant, so…
"
Oh."
"That's right. Servants are hard to defeat even with a Servant. So what should you do?
See, it's such a simple solution. Servants can only exist with a Master. No matter how powerful the Servant is, the Servant will disappear if the Master dies. So…"
That's right, it's a natural solution.
No one would choose to take the hard way.
If you want to win, the most effective way to kill the Servants would be to kill their Masters instead.
"…Okay. I understand that killing the Master is an effective way to eliminate other Servants.
But then, if their Servant gets killed, does that make someone not a Master anymore? Only Servants can touch the Holy Grail, right? Then there is no point to a Master that doesn't have a Servant."
"No, the right to be a Master still remains as long as you have the Command Spell. A Master is a magus that can form a contract with Servants. As long as you have the Command Spell, you can form a contract with Servants.
The Servants whose Masters are killed do not disappear right away. They can stay in this world until their magical energy runs out. If such 'abandoned Servants' exist, a Master with no Servant can form a contract with them. That will allow them to rejoin the war.
That is why Masters kill other Masters. Because if you allow them to live, there is a risk that they will impede you in the future.