reasonable

fallacious, misleading, sophistic (or sophistical), specious

unarticulated

unscientific

absurd, cockeyed, crazy, daffy, fatuous, half-baked, half-witted, harebrained, insane, loony (also looney), mad, nonsensical, nutty, preposterous, simpleminded, stupid, weak-minded, witless

senseless, thoughtless

uncompelling, unconvincing

unsubstantiated, unsupported, unwarranted

flimsy, implausible, unconvincing, weak

fallacious, false, misguided, misled

increased, inflated

exorbitant, extravagant, overpriced, prohibitive, prohibitory, steep, stiff, superexpensive, ultraexpensive, unreasonable

invaluable, priceless

luxurious

brainless, dense, doltish, dopey (also dopy), dull, dumb, fatuous, half-witted, mindless, obtuse, senseless, slow, stupid, thickheaded

fallacious, groundless, illogical, invalid, nonsensical