I do not understand the desire to use force blast when you have penetrating poison.

How about assigning this to a a figure on your force who isn't on their penetrating poison click or doesn't have it at all and force blasting opposing figures into your friendlies WITH the penetrating poison showing!

Well for one, it's only 4 points which is super cheap to get plus one stats on a RL. Second, you could FB someone who is between you and a wall for a knock back damage in between poison turns. It definitely has it's uses.