Sure, let's forget the last word in that sentence "くれえで" = "くらいで" which is the most important.
To not give a long explanation here, Kurai is a word that mainly has 2 uses, 1 is to round. For example when you don't have a certain number for example, like: 20分くらいで着くよ "I'll arrive in 'around' 20 min"(you don't have the number but you know you'll arrive around that time). Or like "It weights 'around' 5 kg"(the same thing), etc. I think it's pretty simple.
Anyways this is not the case here. The other case is similar but at the same time it's difficult to explain why it's similar.
The other case it's to show that it's not that big of a deal. For example そのくらいで騒ぐな(don't make a fuss 'just' for something like that), this is one of the examples but it's basically the same one that Zoro is using.
Zoro says ジジイ一人死なせたくらいで("'Just' because he let 1 old man die").
Also the first sentence, Zoro is talking about Luffy's attitude that Jinbee and Franky were talking about in the beginning of the conversation, yes, it's obviously negative but he isn't talking about Luffy's responsabilities or anything like that, he is talking negatively about him being depressed because of just 1 old man dying despite his position as an emperor.
Edit: Maybe saying that the word is used to show that 'it's not that big of a deal' is a bit wrong because i can think of cases where it's not exactly like that but the same. It's a bit difficult to explain.
To not give a long explanation here, Kurai is a word that mainly has 2 uses, 1 is to round. For example when you don't have a certain number for example, like: 20分くらいで着くよ "I'll arrive in 'around' 20 min"(you don't have the number but you know you'll arrive around that time). Or like "It weights 'around' 5 kg"(the same thing), etc. I think it's pretty simple.
Anyways this is not the case here. The other case is similar but at the same time it's difficult to explain why it's similar.
The other case it's to show that it's not that big of a deal. For example そのくらいで騒ぐな(don't make a fuss 'just' for something like that), this is one of the examples but it's basically the same one that Zoro is using.
Zoro says ジジイ一人死なせたくらいで("'Just' because he let 1 old man die").
Also the first sentence, Zoro is talking about Luffy's attitude that Jinbee and Franky were talking about in the beginning of the conversation, yes, it's obviously negative but he isn't talking about Luffy's responsabilities or anything like that, he is talking negatively about him being depressed because of just 1 old man dying despite his position as an emperor.
Edit: Maybe saying that the word is used to show that 'it's not that big of a deal' is a bit wrong because i can think of cases where it's not exactly like that but the same. It's a bit difficult to explain.
Where did you get the "because" in the sentence?
"Even though he's a Yonkou now, it's disgraceful to think that he could just let an old man die like that."