Pre trib rapture teaching is heresy

[Esaias]

Okay, now that it has been clearly established that the pre trib rapture doctrine is false doctrine, let's examine the question of "is it qualified to be called 'heresy', and what should we do about it?"

First, what is "heresy"?

G139 - heresy
αἵρεσις, εως, ἡ,
I
1. taking, esp. of a town, Hdt. 4.1, etc.; ἡ βασιλέος αἵ. the taking by the king, Id. 9.3; ἐλπίζων ταχίστην -σιν ἔσεσθαι Th. 2.75; αἵ. δυνάμεως acquisition of power, Pl. Grg. 513a: — generally, taking, receiving, ἐπιγενημάτων PTeb. 27.66 (ii B. C.). (αἱρέομαι) choice, αἵρεσίν τ' ἐμοὶ δίδου A. Pr. 779; τῶνδε.. αἵρεσιν παρδίδωμι Pi. N. 10.82; foll. by relat., αἵ. διδόναι ὁκοτέρην.., εἰ.., etc., Hdt. 1.11, cf. D. 22.19; αἵ. προτιθέναι, προβάλλειν, Pl. Tht. 196c, Sph. 245b; εἰ νέμοι τις αἵρεσιν S. Aj. 265; αἵρεσιν λαβεῖν D. 36.11; ποιεῖσθαι Isoc. 7.19; αἵ. γίγνεταί τινι Th. 2.61; οὐκ ἔχει αἵρεσιν it admits no choice, Plu. 2.708b.
2. choice, election of magistrates, Th. 8.89, cf. Arist. Pol. 1266a26, al.; αἱρέσει, opp. κλήρῳ, 1300a19, etc.
3. inclination, choice, πρός τινα Philipp. ap. D. 18.166, Plb. 2.61.9, etc., cf. IG 2.591b; opp. φυγή, Epicur. Ephesians 3 p.62U.; περὶ αἱρέσεων καὶ φυγῶν, title of treatise by Epicurus.
II
1. purpose, course of action or thought, like προαίρεσις, Pl. Phdr. 256c; ἡ αἵ. τῆς πρεσβείας Aeschin. 2.11; αἵ. Ἐλληνική the study of Greek literature, Plb. 39.1.3: — conduct, PTeb. 28.10 (ii B. C.).
2. system of philosophic principles, or those who profess such principles, sect, school, Plb. 5.93.8, D.S. 2.29, Polystr. p.20 W., D.H. Amm. 1.7, Comp. 2,al., cf. Cic. Fam. 15.16.3; κατὰ τῶν αἱ., title of treatise by Antipater of Tarsus; περὶ αἱρέσεων, title of Menippean satire by Varro, cf. Fr. 164; αἵρεσις πρὸς Γοργιππίδην, title of work by Chrysippus, D.L. 7.191; esp. religious party or sect, of the Essenes, J. BJ 2.8.1; the Sadducees and Pharisees, Act_5:17, Act_15:5, Act_26:5; the Christians, ib. 24.5, 14, 28.22, generally, faction, party, App. BC 5.2.
3. corps of epheboi, OGI 176 (Egypt).
4. Astrol., 'condition', Ptol. Tetr. 21; ἡ ἡμερινὴ αἵ. Vett. Val. 1.13.
III
1. proposed condition, proposal, D.H. 3.10.
2. commission, ἡ ἐπὶ τοὺς νέους αἵ. Pl. Ax. 367a; embassy, mission, IG 4.937 (Epid.).
3. freewill offering, opp. vow, LXX Lev_22:18,al.
4. bid at auction, τὴν ἀμείνονα αἵ. διδόντι παραδοθῆναι POxy. 716.22 (ii A. D.), cf. 1630.8 (iii A. D.).

So, the word itself has a variety of meanings, but as used in theology the term essentially means a body of teachings, a sect, a faction, or party. The reason it refers to a sect, faction, or party is because a sect, faction, or party is characterised by it's distinctive body of beliefs/teachings. Thus, the sect of the Pharisees was a distinct sect from other Jewish groups because of the distinctive body of Pharisee beliefs/teachings. From this we can conclude the term essentially means a distinct teaching, belief, etc that creates a distinction.

1 Corinthians 11:16-19 (16) But if any man seem to be contentious, we have no such custom, neither the churches of God. (17) Now in this that I declare unto you I praise you not, that ye come together not for the better, but for the worse. (18) For first of all, when ye come together in the church, I hear that there be divisions among you; and I partly believe it. (19) For there must be also heresies among you, that they which are approved may be made manifest among you.

Paul concludes a teaching on headcovering by noting that there is a unified doctrine and practice amongst the churches of God. He then states that there are divisions and heresies amongst the Corinthians, and says the divisions are the result of the heresies. From what we know of the definition of heresy, we can see how this confirms that definition: There were groups in the church who held to particular beliefs, teachings, practices, that distinguished them from the other groups. The distinct teachings/beliefs creates a "group" or clique within the church, making them distinct or different from the rest of the church because the group holds to a different doctrine. If there are multiple heresies, it would be expected to create multiple divisions, multiple sects, parties, factions etc.

In this sense, pre trib rapture is undeniably a heresy - it is a distinctive belief that creates a division, between those who are pre trib and those who are not pre trib.