I'm going to give him anything, it might as well be something that kills tapeworms since those can be present even with a clean FEC.
They show up eventually - I found that out
That was two years ago and the same horse, out of my four, is the one that needs wormed this time. He used to be my most immune fella but he's now 25, diagnosed with Equine Metabolic Syndrome in 2007 (that knocked the snot out of his immune system), hind gut ulcers, and the vet is suspicious of lipomas in the GI tract.
Given this Fella's health history, my own common sense tells me not to worm him without doing fecals but the vet is adamant that I don't -- and he now tells me what to worm this horse with and when to worm him.
For example we are having some exceptionally cold/raw weather for our area and the vet told me to wait until the next "leveling out of temps" to worm this guy. We're supposed to be in the low-mid 50's all next week, so I will worm him in the AM right before turnout. He has 15 acres to mosey around and hopefully that will keep me from having to get the Banamine out as he now also colics at the mere mention of the word.
That was waaaay more info than the OP asked for but, I feel these exceptions to the worming rules need to be brought up so others are aware "just in case"
I also read a credible article that does say, while Tapes don't always show up, if one has a horse with a weak immune system, it's prudent to keep doing fecals because Tapes will show up eventually -- where's that green throwing up icon?