There are use cases where I would agree with not allowing requests to a local host and yes there is a filter... but this took SO LONG to find. Maybe the error message should inform you of when this happens, because now it just says "A valid URL was not provided". Code in WordPress core: https://github.com/WordPress/WordPress/blob/994b57a1902592d…

wordpress-you-make-me-mad.php

if ( $ip ) {
	$parts = array_map( 'intval', explode( '.', $ip ) );
	if ( 127 === $parts[0] || 10 === $parts[0]
		|| ( 172 === $parts[0] && 16 <= $parts[1] && 31 >= $parts[1] )
		|| ( 192 === $parts[0] && 168 === $parts[1] )
	) {
		// If host appears local, reject unless specifically allowed.
		/**
		 * Check if HTTP request is external or not.
		 *
		 * Allows to change and allow external requests for the HTTP request.
		 *
		 * @since 3.6.0
		 *
		 * @param bool false Whether HTTP request is external or not.
		 * @param string $host IP of the requested host.
		 * @param string $url URL of the requested host.
		 */
		if ( ! apply_filters( 'http_request_host_is_external', false, $host, $url ) )
			return false;
	}
}