I made some vegetarian stew that is way too spicy for my guests... is there anything, besides adding potatoes to absorb some of the spice, that I can do?

try adding some rice as a base. Also, add cold sour cream and cheddar cheese to the top
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Perhaps another way to deal with this is just to take out some amount of the spicy stew, and then add more of the basic ingredients without the spice. You can freeze what you take out for another day. I don’t know about neutralizing Cayenne itself.

honey can make things less spicy, just dont add too much or it will be all weird and sweet. raw potatoes are best for over-salting, although they may work for spices too.

I think I read somewhere that lime juice is one of the ingredients that can kill down the spicyness. I believe that’s for mexican cuisine. Not sure what kind of stew you are making, you can test taste it by putting stew in a bowl and put some lime juice if it would taste less spicy.

Use yogurt as a side dish. Also ice water (in glasses for thirst and burnt tongues).

drain it—sounds like you have enough spice on the main ingredients to be able to use some plain vegetable broth to replace the liquid and it will absorb the spices left on the vegetables.

here’s a rule of thumb. you can add heat or spice in, but you can’t take it out. for novice cooks or those trying new recipes, taste-test as you go. if it’s too spicy from the beginning and you followed the recipe to the letter, your palate will need to adjust over time to that “spicy” factor.