With restrictions the Democrats and some Republicans can put more honest candidates at a significant disadvantage. They oppose this for the same reason they don’t want voter roles purges, lists compared across state lines, and IDs required to register or vote.
The problem with laws is that republican politicians get prosecuted for the smallest violation while democrats can almost get away with murder.
So for republicans, the fewer laws, the better.
If you got all the records on the romney vs. obama campaigns you would find in romney a real effort to comply with all the BS laws while with Obama you would find an effort to hide and cheat and totally ignore following the laws.
Therefore, it will always be in the republican interest to have no laws.