I think the point is that, instead of camping out and waiting for them to get into their cars so they can ticket them, maybe something more proactive should be done to prevent them from getting in their cars at all.
There is, of course, the argument that punishing people that try to drive after drinking too much may get them to change their behavior. Regardless, doing it this way makes one wonder if income from tickets, rather than safety, is the real goal.
I remember when I worked delivering Chinese food, waiting in an intersection to turn left. A police officer was sitting at the light across the street from me. I saw him, turned left and he promptly pulled me over. Turned out there was no left turn at that time of day. I was stunned that he watched me do it and then gave me a ticket rather than warn me, but my care about left turns was much higher because of it. He changed my lifelong behaviour because there was a real consequence (a ticket was very costly to me then at minimum wage). If he'd honked to warn me, I doubt I'd even remember the incident.
About income from tickets vs safety, catching people who are in the act this way is both. It's not like they get the ticket and then let them drive away. When you catch and prevent someone from driving drunk you improve safety as well.
