Things that are poisonous don’t always look that way. Viruses hide. Parasites must, by their nature, hide that nature in order to get close to you.
In other words, not everything that can kill you is obvious about it. The social versions operate the same way.
Some creatures can only survive by feeding on you. Some creatures can only survive by destroying you. And some creatures bear you no ill will at all, but their nature is so different from yours that they’re toxic to you. And all of these people will look like they aren’t those things. They’ll tell you they aren’t those things, and they might even believe that they aren’t those things.
It is up to you to measure them. To hold your own values and your own life in high enough regard to be worth protecting even when the poison comes in an alluring package. We all want friends, relationships, social groups, peers that esteem us. We want those things, so when people come in those guises we are more likely to accept them – to bend ourselves to fit what they want us to be.
And then you have a tapeworm.
Shed the parasites. Give them nothing to feed on, and no room to thrive. Have only noble relationships to the best of your ability, and limit your exposure to the ones you must have that fall short of that ideal. Give your resources fully to those that deserve it (including yourself!) so that you leave no room at the table for the tapeworms.