A friend of mine has gone on a number of solo trips to out of the way and often dangerous places, like Tibet, Burma, Laos, and the less citified parts of Thailand. He's an adventurer and enjoys exploiting her personal resources and skllls to get around in such places. I admire that, but have only been on a few solo trips myself, only interstate in Australia.
Not sure if there is a general stigma against traveling alone, but I can see clear benefits to both sides. When traveling alone, you set your own times and pace, go where you want, whenever you want, and do not need to account for someone else.
On the other hand, traveling with a like minded friend or partner means you have someone to watch your back, someone to confer with about experiences and places, and someone to take care of certain tasks while you attend to others.
I spent three weeks in Japan with a great friend who didn't hold up my photography at all, and his intrepid nature led us to all sorts of places. Being military, his sense of direction and orienteering was excellent, so we found our way around surprisingly easily. From my end, I did most of the translation and talking, and organized all the hotels, flights and other logistics. Looking back, I wouldn't have have done it alone, and I would happily do it all over again.
But I'm often out on photo walks by myself, or going shopping, going to shows or gallery exhibitions, and suchlike. It's at those times when I 'get my Zen on', and the need to attend to someone else, even if they are totally independent, is gone. It allows me to focus 100% on my own experience of photography, just me and the camera and the world around me.
