A really good point has been raised that is practical and applies to the majority of people. What if it is the spouse/live in partner that is toxic? The majority of us do or will one day end up living with a partner and being significantly entangled with them as a result. Primary style entanglements. Joint financial obligations, kids perhaps, family responsibilities. If someone I met had a toxic partner, or a partner that became toxic and they had a primary style relationship in this fashion, and I really loved them or whatever and didn't feel ending the otherwise healthy relationship was a real option, you would be screwed.
Of course you can put up boundaries about the physical and emotional space you share with that person but those boundaries you enforce are more likely to limit the relationship you have with your partner. If you decide never to be in the same room as them, that means you can never go to your partner's house. If you decide to never socialise with them, that restricts you from certain social events that you may wish to attend and therefore, potentially limits the time you could be spending with your shared partner.
It puts limits on the future, the idea of you all sharing a home is not just unrealistic or challenging, it is a complete no no.