Definitely heresy.
What's just as worrying among the (politically) conservative Christians is their idolatry perversion of patriotism. It is just as much bad theology as the (theologically) liberal Christians who decide to ignore or re-interpret any parts of the bible that they don't like.
There are whole large swathes of the Bible that all Christians ignore or re-interpret, re-emphasize or de-emphasize. For some, it's a matter of saving grace with faith that if you let him, God will work in your heart to make sinning more difficult for you. It is the faith that stops the sin, not the other way around.
There are those that believe caning your children until they are black and blue, sequestering them away from the outside world with homeschooling and severe limitation on the people they are allowed to be around with a rigid Biblical Patriarchy in the home governed by laws and rules is the only way to salvation... that God is constantly looking for an excuse to burn you for eternity unless you break your will and turn it over to the chain of command. (Think the Duggars, for example...)
Some people are really terrible at following the commandments and being faithful, but they just
really really hate gay people... especially gay men. And so they become like scorpions... Bible in hand to fight away the sinners but seeking to use the force of government as the deadly sting in the tail that hovers above you, out of sight. This goes for a lot of "Christians" in this country. The ones that like that billboard, most likely.
The rest just pick and choose as they please and don't think about it too much or maybe they think about it a lot. But besides the first group, they're all just the blind leading the blind to salvation.