Lots of people do things lots of different ways. Maybe that guy has kept them that way with no problems, and so he feels confident recommending it to others. If he's a breeder he's also probably far more prepared to deal with the hundreds of babies that will result than most common pet owners are.
They can be fun and social when put together, but when forced to live in the same enclosure dominance issues can arise. There are people who have put dragon's together only to have them fight and cause injury to each other. It's a gamble, and in the end you make the choice what's best for your lizards. I think when it comes to my pets I'd rather be 100% safe than take that chance, looks like you feel that way too. 
Good luck with whatever you choose to do. Beardies are addictive, I myself recently had to get another, it's hard to stop at one!
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1.0.1 bearded dragons (Ocho / Domo-kun)
0.1 kingsnake (Rio)
1.0 ferret (Playstation)
1.0 cat (Wally)
0.1 dog (Tima)