I'm very sorry to break the news to you, but you are somewhat responsible for your own safety. Being the healer does not exempt you from having to make smart positioning choices. Yes the team should protect you, but that's not the only responsibility of the rest of the team. I'm very tired of people playing mercy and raging at the team because they died. If you got sniped, let the team know where you got sniped from. Don't just blindly rage at everyone after you just shifted to our reaper that was in the middle of the entire enemy team. 75% of being a good Mercy is being able to juke the enemy team. Also, pay attention to the enemies team composition. If you are getting focused by a sniper AND a tracer/genji, then is probably time to switch healers. A Winston pick from your team can help counter snipers and tracers, but not both at the same time.