True, but these theories have become popular in the US because within the parameters of the American republic, they're the theories that allow you to step back and say "OK, what did this law
mean?". Other theories involve much more individual interpolation and personal judicial bias/opinion/whatever, which is what is usually meant when people say "legislating from the bench".
The people of the Great State of $YOUR_STATE are reading the bills as they're written and electing, instructing, and/or recalling their representatives according to the contemporary mainline meaning of the actual recorded text of the bill. The people of $YOUR_STATE don't know that $YOUR_SENATOR meant X when he said Y. Or even if they do, there's no way to know that the people of $BORDERING_STATE, who also supported the bill, had the same implicit caveat.
Thus, the only way to understand the meaning of laws enacted by "the People" is to interpret the recorded text as an average person contemporary to its passage would have understood it.
