From the very beginning of the "Peanuts" specials, it's been clear that the makers were very opposed to the commercialism of many holidays. Remember the protest in "It's the Easter Beagle, Charlie Brown" -- "It's Easter and they already have their Christmas decorations up!". So the very cynical view of this holiday, which has been completely co-opted by the greeting card and candy industries, in this special, can't really come as any surprise.
Yet at the same time, the animators do take the time, via Sally's recitation of Elizabeth Barrett Browning's famous poem, to offer a sincere tribute to the spirit of the holiday and the sentiments that it's supposed to be about. Admittedly, they also undercut that by having Linus specifically mention her, and the poem, in his ultimate denunciation of the holiday.
Yet at the same time, the animators do take the time, via Sally's recitation of Elizabeth Barrett Browning's famous poem, to offer a sincere tribute to the spirit of the holiday and the sentiments that it's supposed to be about. Admittedly, they also undercut that by having Linus specifically mention her, and the poem, in his ultimate denunciation of the holiday.