Many New Testament scholars have observed that the conception of the resurrection body implied in 1 Corinthians 15 clashes so violently with that presupposed in the gospels that the latter must be dismissed as secondary embellishments, especially as 1 Corinthians predates the gospels.

By itself, 1 Corinthians 15 just wouldn't mean much. He wants the appearances of 1 Corinthians 15:3-11 to be read as if they had in parentheses after them 'See Luke 24; Matthew 28; John 21.'

Does it take a blanket presupposition for a historian to discount some miracle stories as legendary? No, because, as even Bultmann recognized, there is no problem accepting reports even of extraordinary things that we can still verify as occurring today, like faith healings and exorcisms. However you may wish to account for them, you can go to certain meetings and see scenes somewhat resembling those in the gospels. So it is by no means a matter of rejecting all miracle stories on principle. Biblical critics are not like the Committee for Scientific Investigation of Claims of the Paranormal.

One can believe God capable of anything without believing that he did everything anybody may say he did. One can believe in the possibility of miracles without believing that every reported miracle must in fact have happened.

Though [Charles Guignebert] could not accept either the Christ myth theory, which held that no historical Jesus existed, or the Dutch Radical denial that Paul authored any of the epistles, Guignebert took both quite seriously.

The Holy Bible. Promoting ignorance and superstition for nearly 2000 years.

A critic may reject some miracle stories as legendary, and not others, with no inconsistency at all for the simple reason that even if one holds miracles to be possible, one need not hold legends to be impossible! There are other factors, literary and historiographical ones, that might lead a critic to conclude that even though miracles can happen, it does not appear that in this or that case they did.