On the one hand I don't think the church should be making the law but on the other hand I see law as being set in place by God for the punishment of wrongdoing (see Romans 13).

In that latter respect then any good law has it's origins in God and is likely, I think, to be in harmony with His moral will. In that respect I believe it would promote family and heterosexual marriage. As man/boy sex does not really fit into this agenda I can't see how God would bless such a law.

Romans 1 describes the case of man in rebellion against God and Him basically handing them over to their lusts. Thus any legalisation of man/boy sexing I would most likely see as a "handing over" judgement from God and thus not a good thing.

Further, Eph 2 describes the whole "world" as under the rule of Satan and being by nature children of wrath. I think any legalisation of something that was sinful would have to be a result of Satanic rulership. The harmfulness or lack thereof of the thing would be irrelevant.

In the light of this I am against it.

The law as it stands does not prevent harm. Consensual, loving and otherwise harmless man/boy relationships could be very damaged by prosecution.
Similarly legalising would not remove this chance of harm, since lack of sensure could open the door for all sorts of abuse to be gotten away with.

Law cannot prevent harm. We have so much law and society is filled with harm.... much of it CAUSED by law. Perhaps all of it caused by sin.
Law is not the issue rather it is doing the will of God.

Blessings
Cat.