Interestingly polarised views in this topic.
I think reactions depend on whether you've lived in family houses recently with just 1 bathroom. Obviously in the past, most 3 bed houses just had one loo and people considered it entirely normal. If you grew up in one of those and love in one now, you'll have managed fine and got used to the occasional having to wait and will think it's totally fine and not a deal breaker.
More houses now have more than 1 loo. Houses built in the last 30 years kften have 2 or more loos if they are 2 or 3 bedrooms and lots of people have added a loo or ensuite to houses that previously has just 1 loo. So more and more people have lived in houses with more than 1 loo and that will increasingly be the case as time passes.
In terms of living in a house, if you're a family of 4 or more, having 2 loos is handy and I'd say desirable even though you can manage without.....but crucially, if your budget only stretches to a house with 1 loo in order to get the downstairs space and bedrooms you need, then 1 bathroom is totally fine......you can only have what you can afford.
If you can afford a house with the living space and bedrooms you need and more than 1 bathroom, then only having 1 loo probably should be a deal breaker especially if it's a bigger house. Not only will just 1 loo be less convenient for you but it will make the house harder to sell-on in future ...and people's expectations about having at least 2 loos will only grow rather than diminish.
So, to all the people saying they've only ever lived in a house with 1 loo and have been fine, well of course you have and people will continue to be fine. It's not a total necessity although increasingly common. The issue isn't really about if you can manage with 1, but if you can afford a house in an area which has all the bedrooms and living space you need and would normally have 2 but doesn't. In this case, I think it really is a bit of a deal breaker if there is no possibility to add one. In most reasonable sized houses there will be room and people have recognised there might be space for an Ensuite where the main bathroom is here. This would solve the issue.
If however there genuinely was absolutley nowhere for a cloakroom or an Ensuite and I could afford a similar house, I would turn this one down, in the same way I'd turn down a 3 bed house where 2 of the bedrooms were singles.....because it just didn't deliver the things I personally wanted from a house and coukd afford to have in a different house.