Well, only a bit of it is genuinely bad history, but it's definitely not justifiable. I mean this bit:

25th of December was only chosen because it was the day of saturnalia and many pagans would celebrate on that day so they just changed his birthday to 25th of December.

That's demonstrably false on at least two counts: first the argument that /u/boruno cites, that it's likely that date was a consequence of assigning the date of his death (and hence also conception, by some Judaic traditions) to 25 March; and second, that isn't the date of Saturnalia. This post in the linked thread, by /u/xaxers, gets it right. And, surprise surprise, the voting on the most accurate post there is controversial...

Unfortunately, this bit of boruno's post --

Even though Christianity did borrow pagan dates and activities later in its life, it seems unlikely that it happened in the early centuries:

But we don’t have evidence of Christians adopting pagan festivals in the third century, at which point dates for Christmas were established. Thus, it seems unlikely that the date was simply selected to correspond with pagan solar festivals.

is a mite tendentious. We do start to see evidence of Christians interpreting Christmas in terms of both its closeness to the solstice and its coinciding with a civic festival at Rome for one of Rome's four sun cults, Sol Invictus, starting in a text called De solstitiis et aequinoctiis which probably dates to 4th-century Syria. Here's an especially relevant bit of the text:

But they also call it "the birthday of the Unconquered". But who is so unconquered as our Lord, who underwent and overcame death? Or if they say that it is the birthday of the sun, that is also the "Sun of righteousness" of which the prophet Malachi spoke...

This may be roughly contemporary with or a little earlier than the 354 Calendar, which is the earliest extant source both for the date of Christmas and for the existence of a festival honouring Sol Invictus. It'd be daft to claim that Christmas was modelled on Sol Invictus in any way: in particular, the reference to "the birthday of the sun" is a tendentious interpretation on the part of the author, since the Latin word natalis was used for any kind of civic festival, not for birthdays. But some people of the time did take note of the coincidence of their dates.