As mentioned, I think a better pro-vaccine message needs to be put tut there for sure. But just jumping to "your kid is going to die" is something they already don't believe, so towing that line is not going to convince them.
As BobtheFork has pointed out, I think a better message is to emphasise benefits outweighing risk, with the risk most likely actually being zero (for autism at least). In today's society there are lots of things we continue to use that actually has real life risks, yet we use them anyway, because the benefit far outweighs the dangers.
It's an uphill climb, but using "your kid is going to die, you like kids dying" line is about as effective in convincing them as they are to convincing you that vaccines cause autism.
To be sure, a lot of parents are just super cautious about their kids health, and are misinformed. Not all anti-vaccination believers are the far extreme - some just want to be more safe than sorry, and for them, it may only take that small discussion to let them know that vaccination IS the way to be more safe than sorry.