[TokuChris]

The switch amplifies negative energy and negative emotion.

With Aquarius, we saw jealousy spill in to rage.
With Taurus, we saw anger spill in to total domination.

I think the quote is basically stating that because the switches amplify NEGATIVE feelings/emotion/energy, one can never use the switch for the purpose of doing good things. Aquarius could heal, yes, but she only used the switch when the negative feelings/emotions over-powered her. Same for Taurus. My thoughts are that it's a flaw in Gamou's plan ... he's able to have very fast Horoscope Zodiarts thanks to Libra but the cost is that they are never truly allowed to let the switch push the negativity to the forefront like we saw in earlier Horoscopes.

Zodiart Switch = Increases Negative Energy
More Negative Energy = Stronger Horoscope
Stronger Horoscope = Scorpio, Aries, etc.