Yes, they're bad for your plants -- and judging by all the holes, you've got a major infestation. They do eat fruit as well as foliage ... but you shouldn't worry only about whether they'll damage the fruit, because without leaves, the plant won't have enough energy to have any fruit.

Go to your favorite garden center or big-box store and buy something containing BT -- Bacillus thuringiensis kurstaki. BT kills caterpillars; it won't harm beneficial bugs or bees. DiPel is a common product containing BT. Buy it today, because as the caterpillars grow, they'll be able to eat an increasing amount each day. You'll need to apply it under the leaves as well as on the upper surface. Liquid BT is easier to apply where you want it than the powder.

[Make certain it's BT kurstaki; there are other strains of BT that are effective against other insects but not caterpillars.]

Please don't use a general insecticide like Sevin, as that kills everything.

I used to get lots of tomato hornworm like shown on the current post 'is my tomato ruined' or something. I never had them in a quantity able to do much damage to semi mature plants and they didn't show up until then. If any chewing critter is busy at this stage, it could do serious damage.

"Thuricide BT Caterpillar Control" by "Southern Ag".

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That said, Bt won't work if the things are half grown or older -- too late.

Just try not to use it if your plants are flowering, as the flowers will draw in good insects that will come in contact with it and you'll kill your pollinators.

But if it comes down to nuking it from orbit with sevin just to be sure, or letting a hornworm strip your tomato to the bone, I vote for the sevin.