These are Christian values —
conservatism.
Maybe nice, maybe less so,
but what does that have to do with Judaism?

Which sperm is preferable, that of a Jew or a gentile?
With sperm from a Jew there is concern about halakhic problems if the father is unknown.
With sperm from a gentile, there are views that the child is of doubtful Jewish status (brought, for example, in Tosafot's rulings on Yevamot, but I’ve seen it in other halakhic decisors as well).
Maybe the most optimal option is shared parenting with a Jewish man, or sperm from a soldier who fell in battle.

In my opinion, sperm from a gentile is better. Aside from various mystical ideas, there’s no problem with it.

Even according to the views that the child is of doubtful Jewish status?

Strange views. I wouldn’t worry about them.

By the way, I’m not familiar with such a view. In any case, there’s no reason to be concerned about it.

Y.D., is the child of doubtful Jewish status, or is the donor of doubtful Jewish status? After all, the child follows the mother.
By the way, from what I understand, even from a Jewish donor the child is kosher.
(As for siblings marrying, in a case where there is concern, you can always rule out a biological relationship with a DNA test.)

Yehudit, we’re talking about the child. There is discussion of this view in Pitchei Teshuva, Even HaEzer, siman 4, se'if katan 1:
https://www.sefaria.org.il/Pitchei_Teshuva_on_Shulchan_Arukh%2C_Even_HaEzer.4.1?lang=he

And on the Otzar HaChokhma forum:
https://forum.otzar.org/viewtopic.php?t=51558