I agree with this statement. However, I think that it's often easier said than done. We live in a society where the words "I love you" have so little yet so much value. There's this unwritten yet widely accepted social rule that "I love you" is reserved for family and romantic interests. To some people, it is even taboo to say those words to a friend. It's like "I love you" is a gift that only the people in the VIP section can get, and you have to have a special membership card to even be allowed in that section. On the flip side, when it comes to romantic relationships, the words "I love you" are LOADED. Sometimes, they are perfunctory, tossed around without much thought. Or, they are withheld (or expressed) as a means of emotional manipulation. And sometimes, they are spoken out of obligation, without the actual feelings to back them up.
I think that if you love someone, you should tell them. Just be sure that you mean what you say...be genuine and authentic. Try not to tell them from a place of obligation or manipulation. Express love without expectation. I love you...not because I expect something from you, but because I just do. I love because I am; I exist, therefore I love. To me, that's what all encompassing love, agape, is all about.