You are of course correct in theory--bail is not to be used as punishment. In practice bail and bail amount is often arbitrary.
Studies show there is often little correlation between community entrenchment and small bail. Jails throughout the country are full of working poor waiting for trial, often for months. They can't afford bail amounts.
We need deterrents of any size to curb random murders by drunks driving. 
What this man did to Mr. Courney is no different than random murder. With a murder charge he might get life, in some states death. And no bail.
What is the good in setting high bail in this case and having his support network visit him behind bars instead of in the comfort of familiar surroundings? It is the same as why the sentence should be long: it *may* serve as a deterrent, even if only slight.
Deterrents of any size to curb random murders are a good.
Let's call it what it is, and deny bail for DUI murders. I believe some lives may be saved, possibly yours or mine.