Originally Posted by The Joker
A well written script can always accommodate a love interest organically. It's not a hard task to accomplish. You're looking at the Begins script the way it's written which has no romantic undertones between Bruce and Rachel until the end, where as I said it comes out of nowhere.
Then in TDK it's obvious Bruce wants Rachel as Alfred makes remarks like "Are you interested in his character or his social circle?" when he sees Bruce watching Harvey with Rachel. The way he eyes up Rachel and Dent holding hands at the dinner table etc.
TDK felt like it had a love interest throughout it's story. Begins never did.
Well, I'm saying I don't think Nolan or Goyer particularly wanted to have a love interest in the version of Batman Begins they originally envisioned, in which Rachel's role would have been Harvey. It's well-known that the studio mandated a love interest, which really means they wanted a popular actress to put on the marquee to broaden the audience.
You're right though, they tried to have their cake and eat it too by making her a tow the line between friend and love interest, and her declaration of love did seem to come out of nowhere at the end. They kind of side stepped having to deal with the romance in any way that took up screen time by having it be more of an implied love. To be fair though, it was playing a bit on the trope of guys and girls never being able to stay "just friends" and there always being more under the surface. This obviously isn't 100% true in life, but it often is.
Don't get me wrong though, I'm not the biggest fan of Rachel by any stretch. I'm a Bruce/Selina shipper all the way and always have been.