It undermines the Israeli left since most Israelis, quite rightly, see the bds movement as unfairly singling out and demonizing Israel.
This means that the israeli left have to defend themselves from being associated with movements like bds, which openly support the destruction of the state of israel.
It makes it far harder to acheive change internally and encourages a bunker mentality.
Israel was bboycotted from 1948 to the 1990s. It made no difference then either.