English verbs have moods. In this nicely written article herein
"if it wasn't for..." vs "if it weren't for"
and in the article : Subjunctive Subtitles - The Economist, 25 Sept,2014 (explained) it can be gathered that Subjunctive has lost its ground to indicative because they are almost identical twins.
Yet we must note down the difference to justify the use of BE in the example sentence.
- When we talk about the facts of life the mood of the verb is Indicative. When the speaker wants to convey hope, expectation, order, unreal situation or something in the store of future, the verb is expressed in subjunctive mood.
— Mikes father insisted that he be a lawyer.
a) subjunctive is tricky in the sense it does not have a final "-s" to the 3rd.person singular of the verb.
b) Verb BE is always be in subjunctive (that I be/ that you be/ that he be)
C) Subjunctive is always used with words like 'insist', require, demand, prefer, and with adjectives like 'important', 'necessary', and , in modern English, almost always begins with a that- clause.
The example sentence takes BE in the subjunctive mood on the basis of the foregoing. 'To be' wouldn't be proper here. We may suitably modify it in indicative mood.