So far, I haven't seen any of these issues, though I haven't reached end-game content yet. As a healer, if I let someone die when I could have prevented it, I sometimes get anger directed at me (for good reason). My general rule of thumb is to DPS as much as I can with consideration given to potentialities. As a healer, I'm on the hook if I'm not ready to heal reactively within, say, 0.5 seconds. That's about how long it takes to cancel my DPS spell, turn off CS, and use an instant heal if necessary. So even if a DPS takes a stupid hit and needs healing, I can react in time. All one really needs to take into account is the 5 second recast time on CS. If you turn it on, you're locked out of healing properly for 5 seconds. That's why I cast HoT/Shield on the tank or group before I switch into it. I'm acting on the belief that nothing dangerous is going to happen within 5 seconds. If something dangerous does happen and I'm stuck in CS, then it's my fault if someone dies as a result.
I typically don't DPS at all in raids, except sometimes during DPS checks as necessary. If I have a really good party, I might consider it, but since most raids are not a DPS race, and just a game of careful patience, I don't think the extra clear speed is worth wiping when one player or the whole party suddenly takes a ton of unexpected damage and you either JUST turned on CS (and they end up dying due to the 5 second recast time) or end up running out of MP because of all the DPSing you had done. Maybe this only happens once in every 10 clears, but it's still your fault if you aren't prepared for that scenario by being out of CS and/or conserving MP.