Theres a number of things that don't make sense about it:
- it seems the popular belief these days for FErs is that the earth is an infinite plane. An infinite plane cannot tilt without infinite energy.
- if there was a tilt, it'd be one way, back and forth. The focoult pendulum isn't switching back and forth.. it's swinging with the motion of the earth
- the tilt would mean that while the earth was at the apex of the swing, anything that is acting under "gravity" would be doing so on an angle. So if you held a pendulum out, it'd be tilted.
Well popular beliefs change, so don't take it a given that earth is an infinite plain! It is also a popular belief, as stated, that the earth does tilt, creating tides. Which might be contradicted by other, newer popular beliefs.
And noone said earth tilts only in 1 direction, back and forth. If it were, the pendulum would of course only swing in one direction. It doesn't. That's because earth tilts in several directions, changing the direction of the pendulum.