It's not "chat with 5 guilds at once". If I have "GuildA" and "GuildB" - I can chat with any of them, but members of "GuildB" would never see any messages from "GuildA". So, if I want to gather people for some activity, I have to duplicate my messages for both guilds. If a member from "GuildA" suggests some activity (f.e. DRM/Dungeons/WvW/Raids/etc.) somebody has to forward that message to "GuildB". It's not what I think about when I heard "chat at once".