| > Where? Peter only felt tired because the symbiote was borrowing his body at night.|
Well there is the case of Spider-Carnage, probably the most prominent. Arguably that was due to the symbiote being bonded to Cletus for as long as it was though, fair point. So lets forget him for a moment.
Then you have the case of the black suit as you say using his body when he was sleeping, not a good thing. Clearly the suit was using him for what it needed in doing so. (This also featured in the cartoon Spectacular Spider-Man, the suit wearing him which I found interesting.)
Also there is the effect it had on Brock making him even more nuts than he already was. And also, as I said in previous posts, it takes two to tango... the symbiote was just as keen to destroy Spider-Man as Brock was or else it wouldn't have shared all Spidey's secrets with Brock.
Also the fact that rather than take over its host totally the black suit decided it would just bond, a clear indicator of other symbiotes general hostility to its host organisms, and gives an incling as to symbiotes viewing hosts as lesser life forms there to be used.
Then if you factor in events in the Toxin mini-series, which admitedly I am a bit fuzzy on, that pretty much showed that symbiotes can learn goodness but more or less are bad dudes if left to their own devices. Frank the cop taught Toxin to be a force for good. But even during Toxin's learning, I remember he challenged Frank as to why he couldn't go any further... as in, kill the enemy.
Oh yes... nearly forgot, Spider-Venom in Spider-Girl. Not a very nice guy. Alternate reality I know, but... even so.
Then you have other sources which show symbiotes as aggressive and or dangerous creatures.
The big one being Spider-Man 3.
Then you have the various Spider-Man cartoons. Starting with the 90's cartoon, and lately Spectacular Spider-Man
There is also videogames to consider, Spider-Man on the PS1 and shortly Spider-Man: Web Of Shadows. Both of these games have symbiotes as the main enemy and threat to the city.
True those examples are not the comics... but they are marvel licenced and therefore would have their plots get the ok first.
Just generally when I sit and consider all these factors, it pretty much means that I personally feel that symbiotes can, and usually are, dangerous creatures. Even though the black suit didn't make Spidey blow his stacks like in the cartoon and SM3... when it left him and bonded to Brock, you could argue we saw its true colours then when it wanted to destroy Peter.
Of course, these are just my own musings on the subject of symbiotes and reading between the lines... so to speak.