The higher haste you have, the less time there is spent casting. The less time spent casting, the lessened chance you will be pummeled or kicked. And when casting holy lights, they heal for enough that a crit will always be overhealing, so haste becomes more valuable.
i have 429 haste and loving it, planning on getting up to 500 tho, wont need to stack stam or resil so much since resili got buff i have more than enuff now and my teamates are really good at keeping pressure on other team that 90% of time i am free to hug pillar and dispell.