"soft" and "hard" sounds

[RonButters at AOL.COM]

In a message dated 9/26/1999 11:24:54 PM, ezra_50 at HOTMAIL.COM writes:

<< Learning Spanish in high school, I certainly thought of it in those terms,
esp. since the softer sound occurs before "e" and "i" (i.e. "just like in
English"). >>

I wonder why fricatives seem "softer" than stops (in Spanish) and why stops
seem "harder" than affricates (in English).