First, Pakistan is not taking part in this, what ever KSA ask doesn't matter. I only care about Pakistani side.
Second, we are defending KSA from who ever attacks, whether these rebels, or some external force like Iran, ISIS or Israel like we always do.
Third, read the background of this whole game, these rebels are the same people who created mess in 2009 in KSA, ryadh, taif, which was cleaned only once Pakistani SSG came into action. Also, its Yameen President asking for help from KSA, so legally KSA is on the right side, and Whole GCC is involved in this not KSA alone.
So no its not aggression, and its not killing all yameeni people but only mess creator. Stop defending the oppressors.