It would seem to me that the real heretics are precisely those that desire now a new law (orthodoxy) to replace the old one. 

The problem is, Sam, that you’ve just drawn up another boundary line and declared some inside of it, others out. You’ve just proposed your interpretation of where the lines of orthodoxy should be: with those who don’t draw lines of orthodoxy!!

Part of the resolution to this paradox lies in understanding how Paul approached Torah — from a Jewish perspective. Like Jesus, his goal was to show how Torah, whch means Teaching, not Law, was transformed by the Messiah, who reorientated it around himself and provided a new hermeneutic in so doing. 

There will always be a cultural element to our hermeneutics — our way of reading scripture. The generous orthodoxy is to be agreeable on major points of agreement, with communities or representatives of whatever conviction. It doesn’t lie with trying to eschew our own convictions, but in tempering them by holding them in tension with what others believe.

With respect to your particular concern here then, Sam. those whose practices you hold in contempt are not to be regarded as heretics — to be rejected — but as "the Other" whether individual or community, who / which is in a much need of redemption as you and I / our faith community.

It is usually when we feel threatened by the Other that we feel the need to draw up boundary lines that keep people out. But as Peter intimates, it is possible to propose boundary lines that are intended not to keep people out but to clarify that which defines the new area into which they are invited. 

shalom! - john (eternalpurpose.org.uk)