The Internet does seem to be full of hysterical web sites claiming it's all satanic and evil.
http://www.nazarite.net/evil-holidays.html
Others seem to say it is a modern celebration invented by an American woman.
This stuff about it being Greek or Roman sounds convoluted and unlikely to me.
The first line of "Valentine's Day" tells me that it is American - "honor" instead of "honour"!
I have come to treat anything written by Americans on the subject of paganism with the utmost contempt.
If you wish to see American Christian stupidity and ignorance and insanity at its worst I suggest that you look up the American comments and commentaries on Harry Potter. The one that had me laughing until I cried was one that stated that Harry Potter was the Devil, Draco Malfoy was Christ and his father, Lucius, was God!
There were, whether there still are I don't know, I haven't looked in ages, over 200,000 American sites on the subject of Harry Potter as Satanic propaganda!
Some of the American fundamentalists make Sassy, ~TW~, Alan Burns and Hope seem total kittens.