Display user meta data from a textarea as a formated text

Have a look at both functions esc_attr() and esc_html()

Replace this one :

add_shortcode('USER_META', 'user_meta_shortcode_handler');

function user_meta_shortcode_handler($atts,$content=null){
    return esc_html(get_user_meta($atts['user_id'], $atts['meta'], true));
}

with this :

add_shortcode('USER_META', 'user_meta_shortcode_handler');

function user_meta_shortcode_handler($atts,$content=null){
    return esc_attr(get_user_meta($atts['user_id'], $atts['meta'], true));
}