This is a very good question DH.
As you can see in the translation on TWTY, it doesn't have the words "in my name", but instead has "on the basis of and upon My ... name". This is because, as the article has stated, it is the Greek word επι/epi which first and foremost means "upon", i.e., putting something "epi/upon" a shelf. It can also mean a whole bunch of other things such as on, at, by, before, against, over, across, opposite, contrary to, near, in the presence of, on account of, for, over a period, for the purpose of, toward, during, in the time of, under a rule, close proximity to, beside, alongside, in power over, control over, have authority over, about, concerning, in the direction of, in benefit of, in order to, in view of, up to, when, at the time of, regarding, with reference to, as well as few more meanings which I really won't have the room for here.
This is also the case with other prepositions such as εις/eis, εν/en, and κατα/kata. To say that "one translation is better than the other" when it comes to prepositions is really based on the context.
However, I actually agree with the article in that it could quite probably mean "against, contrary to, in opposition to", but then this is probably one of those times when a dual meaning is intended. Not only shall there be many people who come "upon the basis of" the Messiah's name, as in, they say that what they're doing is from the Messiah, but that there shall also be many people who come "against, contrary to and in opposition to" the Messiah's name, saying that things aren't from Yahuweh when they actually are.
The article is also right to point out that "in" is not a great translation of επι/epi in this verse. Checking the other Synoptics who have this speech of Yahushua in them, Marcus also uses επι/epi (Marc 13:6), but the oldest Papyrus to contain Matt 24, Papyrus 70, actually has εν/en compared to later manuscripts that have επι/epi in the verse (Matt 24:5).
Nevertheless, this still doesn't explain why English translations use "in" in Lucus 21:8. The only legitimate place they could have "in" would be in Matt 24:5, but they actually base their "translations" on the Nestle-Aland Greek NT, which uses επι/epi and not εν/en.
Hopefully that answers your question