popa- we disagree. The border between halachic matters and non-halachic matters can be hazy but many things are very obvious. Why it should be ‘apikorsus’ escapes me.
Btw- shemita is well covered in the Rambam and has many halachic ramifications. Heter mechira is a legitimate halachic tool, so , for the ones who accept it, it is fully allowed by halacha.