Question about irrelevant conclusion fallacy

There's this classic example of irrelevant conclusion fallacy about legislate on housing. Then a legislator comes in and says that the law should be approved because everyone deserves decent/dignified housing. 

What i don't understand is, why is this an irrelevant conclusion fallacy? I saw this at Introduction to Logic by Copi. 

What's the point of this discussion? In the book it says that the point is the particular proposals/measures. But at least for me, i can't know the exact point of the discussion with the introduction to it.

What i understand is that, it's implicit that the law's point is legislating for decent housing, and that the point of the discussion is not about that right but how the people is gonna get that right, and if the proposal is really efficient with that. 

Am i right? I would like an explanation on why this is an irrelevant conclusion fallacy. It doesn't matter if the explanation is large. And forget that, i would like an extensive and clear explanation. 

Also, sorry for my english, i'm not native. Thanks.

The example of the fallacy is on the book i said before by Irving M. Copi.

I am not familiar with that specific fallacy. It sounds to me like a synonym for a non sequitur . From what I understand, the argument goes something like this:

P1: (housing law here)

P2: Everyone deserves good housing.

C: Therefore, the law should be approved.

The second premise is an opinion, and doesn't help the argument advance. What we re missing, assuming the opinion is shared by the arguers, is HOW the law will result in people getting good housing. We are also missing arguments against the law and disadvantages for passing it. We need that part of the argument before we can conclude anything.

Always check your premises. This seems to have a major premise of “everyone deserves decent/dignified housing.” The proponent must first establish that premise, or it should be the focus of the discussion. Otherwise, I'd put it closer to non sequitur.