Not all the titans are smileys.
For example the one that ate Thomas in the Trost arc was not smiling.
Same for others titans with "strange face" but not smile.
Then I think it's only a way for the author to make the titan more "creepy".
Ya ya your usual japanese creepy theme , although come to think of it I'm having certain trouble or difficulties..... about being in the dark seriously nothing even made me twitch as the titan who ate eren's mother actually i can't go to dark places in the night nor sleep comfortably especially since my house looks like an abandoned house in the night or maybe its just me hallucinating I really GOtta stop watching that first episode GIVES ME THE CREEPS! OMG why did i watch this anime in the first place!?
This is my best hypothesis, considering the fact that were divulged so far.
I believe Reiner, Berthold and Annie come from an underground village of shapeshifters, located outside the outermost wall, where everyone was a shapeshifter from birth (i.e. it's a genetic trait) and where it's a common belief that humans cannot become shapeshifters, under any circumstances.
They grew up as soldiers there and were ordered to bring down the human walls. Apart from being ordered to do it, they are able to do this because they consider humans inferior and without hope of ever seriously engaging with the titans. However, everything changes once they discover Eren, a human turned shapeshifter...
But if they are human-shapeshifters and their aim is killing titans , don't you think they would help the humans ? i mean if they are humans , they do have compassion for their kind , what i think ? actually i can't come up with anything not close to this , i think the first titan that appeared the one that killed moses , that guy is somekind of boss , he is bald , he has scars ! never seen anytitan like him not to mention him not bothering with them around him and not die after hit in the nape of the neck , from the looks of it things like this are plot points in the future , if we can understand his purpose then we understand the rest , although like you said reiner spoke as if humans are bugs or insects , their lives didn't matter to him , but im really sad berthold is bad , he looked so defenseless , i can't believe he ate that guy , this thinking is killing , when is the next chapter coming out any way ?
Imo Reiner, Berthold and Annie are not nazi-like soldiers. They wanted to kill all the people inside the walls for a revenge feeling. Probably cuz the people who live out of the wall have a big grudge against them for some reason.
If you check others threads you will find some speculations about who built the wall: rich and important people that leave poor people behind them being eat by the titan while they flee into a "promise land beyond the sea". And probably the rich people was the first cause of the titan problem itself.
I know , i saw all that but reiner said that he was stupid to act on orders and that they were brats not knowing anything that means he was a blind soldier obeying commands , if you saw the new cover for chapter 46 , eren gets presented to the ape titan , that is what i came out of the pic , at any rate , I don't think there was anyone living outside the wall before 100 years ago maybe before 107 but thats it , the titans are alot more than humans , they would have found out the villages , don't believe anyone who tells you anything , titans seem to find people if they are numerous and they never get tired so sooner or later they were gonna find them , what confuses me tho about how did ymir attack reiner and berthold that is the most confusing thing for me till now , at any rate i heard the next chapter is supposed to come by this week end or next at most , cheers up m8 '-' !