Locking up men does nothing more than keep them off the streets.
要翻译这句话，首先要理解下面两个短语的意思：
nothing more than
可以翻译成就是，不过是

If you say that someone or something is nothing more than a particular
thing, you are emphasizing that they are only that thing, and nothing more
interesting or important.

keep sb off the streets.
直译就是使某人离开街道。
但是它的引申义是：使某人远离坏的事情

This depends on the context of that particular family, but there are three
possibilities:

“…so that you won’t become destitute and sleep in the street?”
“…so that you won’t join a gang and engage in street crime?”
“…so that you won’t become a prostitute and find clients on the streets?”

所以整体这句话的意思就是：
把一个人锁在家里，就是让他远离麻烦。

https://www.collinsdictionary.com/dictionary/english/nothing-more-than
http://forum.wordreference.com/threads/the-meaning-of-to-keep-someone-off-
the-streets.2559569/