The best replacement for heresy is blasphemy.

The best alternatives to heresy are rated as following:
★★★★★  blasphemy
★★★★★  orthodoxy
★★★★  hearsay
★★★  forte
★★★  apostasy
★★  kg4
★★  schism
★★  cornwall
★  heterodoxy
★  heresy
★  bose 901
★  rogue trader
★  sacrilege
  heterodox
  deathwatch
  roman inquisition
  jbl l100

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Speaking about heresy, one probably shouldn't forget about galileo.

Other search terms related to heresy and their ratings are:
★★★★★ galileo
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Google Trends

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heresy
blasphemy
orthodoxy