Sure it could.
On a general level, there's the matter of reputation: each guild has others it likes and dislikes. This means that by joining two or three guilds, you stand a better chance of joining a couple of guilds which don't mesh well. This will lower your rep with those guilds, and make services more costly.
On a more specific level, some guilds give out quests that require stealing from or killing members of other guilds. (There are even a few instances where you steal from your own, but let's not go there.
) Remember that oath you took? If you kill a member of your own kill to satisfy another guild's requirements, the first guild is going to be very pleased.
Still, on the other side, why not? Join however many you want. It's still just fun, correct?
Guilds question 
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