There's no valid reason to not believe Scripture LITERALLY AS POSSIBLE. Sure, there's some symbolism in Scripture, but those symbols always stand for something real. And many of them are explained by other verses of Scripture, while the meanings of the others can be discerned with our overview of all Scripture.
Partial preterism ignores these words of Jesus: Matt. 24:29[i\ “Immediately after the tribulation[/i] of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. 30 Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. "
So we see that Jesus will return immediately after the great trib. Now, if the trib was in 70 AD, He is long-overdue!
As for Matt. 24:34, we must look at the various meanings of "genea", rendered 'generation' in that verse. Besides meaning the body of all mankind living in a given time, it can also mean an age or a nation or people. (We might get a little help on this from the readers of Koine Greek on this site.) And it's quite-obvious that Jesus' use of that word is in a sense other than referring to the people living at the time He uttered that prophecy. Remember, Jesus' prophecies will be fulfilled to the letter of how they were originally written and preserved. And it's just-as-obvious He has NOT yet returned in the manner HE HIMSELF described - in great power and glory, SEEN BY ALL, even those who pierced Him.
Also, remember that over a hundred Old testament prophecies about Jesus' first coming were LITERALLY fulfilled TO THE LETTER. Thus, there's no valid reason to believe the rest of His prophecies won'y be fulfilled just-as-exactly, just-as-literally!
Preterists try to fill in the gaps between their pronouncements and history/reality by reducing "inconvenient" Scriptures to "figurative/symbolic" status, but that's tampering with God's word by inventing new meanings for it - in other words, it's EISEGESIS, that is, reading man-made meanings into Scripture. I have but one conclusion to draw about preterism, full or partial -
"PRETERISM - PHONY AS A FORD CORVETTE!"
TRY READING TRUE GREEK EXPERTS, OTHER TRANSLATIONS AND BAPTISTS OF THE PAST!
The BDAG Greek-English Lexicon
"...the sum total of those born at the same time, expanded to include all those living at a given time and freq. defined in terms of specific characteristics, generation, contemporaries (Hom. et al.; BGU 1211, 12 [II B.C.] ἕως γενεῶν τριῶν); Jesus looks upon the whole contemp. generation of Israel as a uniform mass confronting him ἡ γ. αὕτη (cp. Gen 7:1; Ps 11:8) Mt 11:16; 12:41f; 23:36;
24:34; Mk 13:30..."
The AMGL Greek-English Lexicon
"...of all the people of a given period:
Mat 24:34, Mar 13:30, Luk 21:32..."
The Thayer's Greek-English Lexicon
"...the whole multitude of men living at the same time:
Mt.xxiv.34; Mk.xiii.30;... Lk.xxi.32..."
"Truly I tell you: the present generation will live to see it all." (Matt 24:34, REB)
"I tell you in solemn truth that the present generation will certainly not pass away without all these things having first taken place." (Matt 24:34, Weymouth - Baptist)
"I solemnly say to you, the present age will not pass away before all this takes place. (Matt.24:34, Williams - Baptist)
The Baptist Charles H. Spurgeon
Verily I say unto you, this generation shall not pass,.... Not the generation of men in general; as if the sense was, that mankind should not cease, until the accomplishment of these things; nor the generation, or people of the Jews, who should continue to be a people, until all were fulfilled; nor the generation of Christians; as if the meaning was, that there should be always a set of Christians, or believers in Christ in the world, until all these events came to pass; but it respects that present age, or generation of men then living in it; and the sense is, that all the men of that age should not die, but some should live
till all these things were fulfilled; see Matthew 16:28 as many did, and as there is reason to believe they might, and must, since all these things had their accomplishment, in and about forty years after this: and certain it is, that John, one of the disciples of Christ, outlived the time by many years; and, as Dr. Lightfoot observes, many of the Jewish doctors now living, when Christ spoke these words, lived until the city was destroyed; as Rabban Simeon, who perished with it, R. Jochanan ben Zaccai, who outlived it, R. Zadoch, R. Ishmael, and others: this is a full and clear proof, that not anything that is said before, relates to the second coming of Christ, the day of judgment, and end of the world; but that all belong to the coming of the son of man, in the destruction of Jerusalem, and to the end of the Jewish state.
The Baptist John Gill
Verily I say unto you, this generation shall not pass,.... Not the generation of men in general; as if the sense was, that mankind should not cease, until the accomplishment of these things; nor the generation, or people of the Jews, who should continue to be a people, until all were fulfilled; nor the generation of Christians; as if the meaning was, that there should be always a set of Christians, or believers in Christ in the world, until all these events came to pass; but it respects that present age, or generation of men then living in it; and the sense is, that all the men of that age should not die, but some should live
till all these things were fulfilled; see Mt 16:28 as many did, and as there is reason to believe they might, and must, since all these things had their accomplishment, in and about forty years after this: and certain it is, that John, one of the disciples of Christ, outlived the time by many years; and, as Dr. Lightfoot observes, many of the Jewish doctors now living, when Christ spoke these words, lived until the city was destroyed; as Rabban Simeon, who perished with it, R. Jochanan ben Zaccai, who outlived it, R. Zadoch, R. Ishmael, and others: this is a full and clear proof, that not anything that is said before, relates to the second coming of Christ, the day of judgment, and end of the world; but that all belong to the coming of the son of man, in the destruction of Jerusalem, and to the end of the Jewish state.
The Baptist John Broadus
This discourse certainly foretells in the outset the destruction of Jerusalem (e. g., Matthew 24:15-21, Matthew 24:34); and in the conclusion certainly foretells the final coming of our Lord, with the general judgment of mankind and the resulting permanent state of the good and the bad, (Matthew 25:31-46) in a way substantially equivalent to the predictive descriptions afterwards given by the apostles.
Matthew 24:34. Verily, I say unto you (see on "Matthew 5:18"), calling attention to something of special importance. This generation, as in Matthew 23:36, also Matthew 11:16, Matthew 12:41 f.; and compare Luke 17:25 with Luke 21:32. The word cannot have any other meaning here than the obvious one. The attempts to establish for it the sense of race or nation have failed. There are some examples in which it might have such a meaning, but none in which it must, for in every case the recognized meaning will answer, and so another sense is not admissible.