So the general consensus is that loud girls tend towards the obnoxious side and are simply grabbing for attention by raising their volume levels.

But what about a girl with a loud laugh--when she's genuinely laughing, it happens to be loud--is that such a bad thing?

No it is not a bad thing to laugh loud.
Laughing is a natural anti depressant.

I love it when my wife laughs she sounds like fire engine.
When she is happy I know that she is having a good day.

Might catch some off guard but no big deal for the most part. If its really, really loud she/you/whomever might need to learn to tone it down some for more formal settings (like business/work/etc) but we create enough needless self-conscious noise around ourselves... why fret over genuine laughter?

Certainly nobody should categorize someone because of a loud laugh.

And on the talking note... I know a guy who talks REALLY loudly... he works around construction with ear protection, and he's used to really putting his lungs behind it to be heard... so even the loud talking shouldn't be used to label someone... not to mention some voices are simply easier to hear than others.