“There is possibly a big difference between this scenario and one where the boy decides on his own to grow his peyos. Then, since it was not part of his chinuch (meaning his parents didn’t give them to him, or at least encourage it or praise the change), they are more likely to come off.”
I’m not sure I would agree with that assessment. I think, in the case we’re talking about, the boy will never interpret them a really being meakev since his father didn’t have them. Whereas, someone who becomes more frum and decides to grow them out will see it as being halachically based rather than a seemingly random shtick they were raised with.
I’m not denouncing the trend at all. I’m just agreeing with the posters who have asserted that it’s really just a trend, not a shift is halachic shittah.