We already have (partially) socialized medicine; just the worst form of it.
If you're saying "people without heath insurance can just go to the ER!", you've already conceded the argument. You've admitted that people should have health care regardless of ability to pay. Now, you're just insisting on the least effective and most expensive way to pay for it.
To put it another way: you've agreed to help pay for your buddy's tractor repairs. But instead of chipping in for oil changes and regular maintenance, you're insisting he wait until the engine seizes up and the transmission drops before you'll give him a dime.
An addendum: To say nothing of the fact that certain long term or chronic conditions (cancer, MS, Parkinson's, to name just a few) can only be ameliorated by preventative care - once it's reached "emergency room" levels, it may be too late, and long term damage is already done.