The Marcionites not only rejected the Acts of the Apostles but all the claims associated with it which make up 'the history of the Apostolic Church' for mankind ever since. Yes, it is true the scholarly study of Christianity needs 'red meat.' It needs a historical person named Jesus and twelve apostles and all the 'connecting tissue' embodied in Acts so as to explain how this religion came to be. But the underlying reality which no one seems to want to acknowledge is that the Marcionites thought our inherited version of history was bullshit.
I don't know what that means for the personal faith of scholars and I don't really care. As serious-minded people we have to come to accept the fact that there is nothing which proves the historicity of the Acts narrative other than the belief of billions of inconsequential people. Indeed the outright rejection of this 'spurious' narrative by the Marcionites should be enough to at least suspend our reliance upon this text when discussing the followers of Marcion.
Tertullian actually reveals to us the barest outline of the Marcionite worldview but few in scholarship are willing to listen to what he has to say. Over and over again he says that over a century separated Jesus and Marcion, one hundred and fifteen and a years and a half a month between Jesus and his awaited Paraclete. The formula bears an uncanny familiarity with things said by Manichaean and Islamic apologists and detractors. Scholars uncritically speak of 'Marcion's devotion to Paul' when in fact they are being confused by two different paradigms - i.e. the original postponed 'Paraclete revelation' associated with the figure of 'Marcion' leader of the Marcionites now entirely mixed together with the Catholic presumption of an 'apostolic grounding' of Paul in the years leading up to the first Jewish war.
The reality of course is that the revelation which is described in 2 Corinthians chapter 12 could have happened at any time. The person of Paul is so wispy that the Clementine literature can identify him as Simon. Irenaeus has to repeatedly implore his audience to accept even the most basic tenets of the Catholics - i.e. that there was an apostle named Paul, that Luke was his chosen disciple, that the third gospel was 'Paul's gospel' etc.
To this end it is of the deepest significance that we see Celsus a prominent pagan figure of the middle second century employ the terms christianismos, ioudaismos, christianoi and christianos. It suggests to me at least that he was very close to the Roman figure in the Imperial court who coined these terms. Just look at this statement near the beginning of Book Two of Origen's refutation against Celsus.
He next proceeds to say, that the dogma, viz., Judaism (ἰουδαϊσμόν), upon which Christianity (χριστιανισμὸς) depends, was barbarous in its origin. And with an appearance of fairness, he does not reproach this doctrine (τῷ λόγῳ) because of its origin among barbarians, but gives the latter credit for their ability in discovering (such) doctrines.
Is this Origen summarizing what Celsus says using the terms 'Judaism' and 'Christianity' or do the terms come directly from Celsus's writings? I think the latter especially given the fact that Origen rarely uses these terms and χριστιανισμὸς appears over ninety times in Against Celsus.
If Celsus is the one who coined the term Christianity (or stands very close to the Roman bureaucrat who did) the basic logic of 'heresy' in the writings of the Church Fathers may easily be explained to have derived from official Imperial policy in the second century. Just think about it for a second. Up until the middle of the second century there wasn't even such as a thing as ἰουδαϊσμόν. As Origen notes there countless Jewish sects despite the fact that they all used Moses's Law. Suddenly in the second century the idea of 'normative Judaism' is born or ἰουδαϊσμόν. This developed in the immediate aftermath of the Bar Kochba revolt. No more Sadducees, no more Pharisees - just ἰουδαϊσμόν.
Now when we look to Origen's discussion of Celsus's lost book, it is unfair to describe it as being 'against Christianity' per se. Celsus is arguing on behalf of what he called 'the great Church' which is associated with 'the multitudes.' He is specifically against sectarianism and ritual secrecy of any kind. The idea that a Christian Church Father like Polycarp or Irenaeus just decided arbitrarily to identify all the different sects as 'bad' and the greater Church as 'good' is utterly meaningless. This must have been going on for centuries in Judaism - i.e. in fighting between the various sects. Only when an Imperial official or his spokesperson like Celsus did so with terms like ἰουδαϊσμόν and χριστιανισμὸς - i.e. officially tolerated groups - does any of this arbitrary terminology making have any teeth.