Nah; if your credence in X went up when you read the new reasons, and more importantly if it would have gone down if the opposite of these reasons were true, it's kosher.

If someone challenges your post and you think "Crap, my case doesn't look impressive enough" and selectively search for citations, you're lying.

A grey area is when you believe X because you heard it somewhere but you don't remember where except that it sounded trustworthy. You can legitimately be pretty confident that X is true and that good sources exist, but you still have to learn a new fact before you can point to them. The reason this isn't an outright lie is that trust chains need occasional snapping. There's an odd and interesting effect - Alice distorts things just a tiny bit when she tells Bob, which basically doesn't affect anything, but Bob doesn't know exactly what the distortions where so the distorsions he adds when he tells Carol can be huge, though his beliefs are basically correct! (A big source is that uncertainty is hard to communicate, so wild guesses often turn into strong claims.)

No. Information really is useful for influencing others independently of its use for actually making decisions. It is only the decision making component that is useless after you have already made up your mind.