Yeah but it seems your "aura" won't be evil if you're not completely rotten to the core. It seems Oda makes a distinction between being unredeemable evil and having bad intentions. Pudding was not rotten in the way a Caesar Clown is but she did trick the straw hats and genuinely planned to kill Sanji.
So I don't think Luffy being initially friendly with Loki shot down any chance of him being antagonistic, at least until he gets a sad flashback and Oda have Luffy punch the edge out of him lol. I don't think Loki is joking when he talks about destroying the world (even if the reason might be to rebuild a "better" world)
People mixing up the "sun god" personality with being good or evil.
Imagine someone bad eat Nika fruit and just smile all day but had evil thoughts.
Because him smiling doesn´t mean he is not evil.
In fact that is what Oda tries to show, both Loki and Luffy could have similar personality, Loki more evil thought.
But this is all over again the "Mirror Katakuri vs Luffy" situation, both call themselve the sun god, but we just have one.
Loki laughing doesn´t mean much, this guy killed his father for a fruit.
And he try to destroy Elbaf.
I doubt Oda can build up a better hype for some other Giant at this point when Elbaf literally need all soldiers to just stop Loki alone.
The fact that Oda mentioned his legendary df shows that Loki will fight and show that legendary df.
And it wont be a small showcase, it will be afull blow battle and this only make sense against Luffy...