"Essentially a motte-and-bailey"

A M&B is a medieval castle layout. Those bloody Norsemen immigrants who duffed up those bloody Saxon immigrants, wot duffed up the native Britons, built quite a few of those things. Something, something, Frisians, Romans and other foreigners. Everyone is a foreigner or immigrant in Britain apart from us locals, who have been here since the big bang.

Anyway, please explain the analogy.

(https://en.wikipedia.org/wiki/Motte-and-bailey_castle)

https://en.wikipedia.org/wiki/Motte-and-bailey_fallacy

Essentially: you advance a claim that you hope will be interpreted by the audience in a "wide" way (avoid = eliminate) even though this could be difficult to defend. On the rare occasions some would call you on it, the claim is such it allows you to retreat to an interpretation that is more easily defensible ("with the word 'avoid' I only meant it reduces the risk, not eliminates").

From your link:

"Motte" redirects here. For other uses, see Motte (disambiguation). For the fallacy, see Motte-and-bailey fallacy.