motte-and-bailey

arguer conflates two positions that share similarities, one modest and easy to defend (motte) and one controversial and harder to defend (bailey)

The arguer advances the controversial position, but when challenged, they insist that they are only advancing the more modest position.

Upon retreating to the motte, the arguer can claim that the bailey has not been refuted (because the critic refused to attack the motte) or that the critic is unreasonable (by equating an attack on the bailey with an attack on the motte).

Alice: I don't understand why people believe in astrology; there's no scientific evidence to support it.
Bob: The moon has enough pull to cause tides every day on Earth, but it has no effect on people? Are you trying to say humans are literal gods unaffected by nature?

Here, Bob has substituted an easy-to-defend motte (that human beings are affected by natural forces, including the Moon's gravity) for a controversial bailey claim (that astrology can use the positions of celestial bodies in the sky to make scientifically valid predictions about people's personality, characteristics, and behavior).