I think it's a bad idea. The newcomers who don't understand the point in that would think that's the way this site is and either leave to avoid it or jump in at any time acting like that. It's like opening the gate for chaos and telling everyone to be mean, cruel, etc.
People do need to vent, but they don't need to do it here. They should get punching bags, adopt a work-out schedule, do something active. It's healthier, it's better for this site, and it's better for their body.
For the people who, for one reason or another, do need to vent on this site they can do so without breaking rules. I have done so various times and still do on occasion. I just say what I think minus the swear words and insults. It's not as hard as some people want to believe.