Part of it is surely that he's not (as far as we know ) a Sharran, and unlike Shadowheart I don't think he actively tries to stir up distrust against other party members. But I guess it's largely because, once he does open up, I believe him and don't see any obvious point of conflict in what he wants and what I, or my characters that would have him in his party, are likely to want to achieve.
Now that's an interesting point because, once again, it speaks to the distance between Gale's words and his actions. He repeatedly declares his love for Mystra but what he is doing is heretical to Mystran belief. Mystran faithful, especially the chosen and the magister are expected to author new spells and to create more artifacts. A good Mystran wants to increase the amount of magic in the world. Gale is doing just the opposite - he destroys artifacts. In his words he worships Mystra but in his deeds he worships Shar. Gale is either on the edge of a conversion or someone who worships Shar but doesn't realize it - he's another candidate for chosen of Shar
This is the magister not the chosen but the responsibilities overlap:
Quote
The central task of the Magister was to spread the use and teaching of magic, encouraging its use, and promoting its availability and utility. Specific Magisters sometimes received different tasks, but the common thread was always spreading magic
Love magic for itself. Do not treat it just as a weapon to reshape the world to your will. True wisdom is knowing when not to use magic. Strive to use magic less as your powers develop, for often the threat or promise of its use outstrips its actual performance. Magic is Art, the Gift of the Lady, and those who wield it are privileged in the extreme. Conduct yourself humbly, not proudly, while being mindful of this. Use the Art deftly and efficiently, not carelessly and recklessly. Seek always to learn and create new magic.
And note which items seem to satisfy Gale's hunger - he's satisfied either by ones that cause problems for the party (iron flask) or destroy the works of the good and neutral gods (sword, amulet, idol)
"Are you Sharran but don't know it yet? Take this quiz to find out!"
i do agree your argument. your insight sees through gale. you explain why mystra give up gale.