Is heresy a subject loving Christians should be concerned about?
Yes. Christians are open to false teaching and being lead astray, if you think you are not then tread carefully. 1Cor 10:12.
Peter had to be corrected  by Paul about circumcision being binding on gentile believers. Was Paul wrong for doing that? Many Christians misinterpret the scripture when it say " Judge not" (Matt 7:1-5) The meaning here has to do with not being a hypocrite, ie don't judge someone when you do the same thing.

See article here by Jacob Prasch call judge not.

Here are some links to good articles and media on heretical teaching, saying what they are, why we should avoid such teaching etc.

The Shack

The Emergent Church

Link 1 
Link 2
Link 3

Rick Waren and the purpose driven concept

Link1  Link2  Link3  Link4  Link5