Can't parse your interpretation.
The "guest" was the "domestic abuser" in marriage #1.
He killed his wife.
You don't get more violent than that, and it certainly warranted his arrest.
In the marriage we observe on screen (let's call it marriage #2), there is some mutual emotional abuse, although one might argue that the husband was more aggressively abusive in his extra-marital affair and his apparent disdain for the wife.
We are supposed to believe they have rediscovered their love through this experience, but in real life social terms, most likely this new affection will dissipate and revert to old patterns quickly.
Hitchcock was not ahead of his time in his understanding. In fact, many of his screenplays exhibit some misogynistic overtones.   See 1 other reply