"As proposed by the Amethyst Initiative, to lower ("lowering" is
better) the current MLDA is a difficult topic to discuss."
sounds like the Amethyst Initiative has proposed that the topic is difficult to discuss.
"Lowering the current MLDA, as proposed by the Amethyst Initiative, is
a difficult topic to discuss."
is certainly clearer in this regard.
However, it is not clear why you are discussing the difficulty of discussing the topic, rather than the (complexity of) the issue/action/process itself. If this is what you want to do, then the second sentence is fine. But do you not perhaps mean something like:
"Lowering the current MLDA, as proposed by the Amethyst Initiative, is
a controversial issue."?
or
"Lowering the current MLDA, as proposed by the Amethyst Initiative,
would be a complicated process."?