People are more likely to trust strangers when they have had a reason to work with them. That is part of the appeal of a shared period of service for young adults: people from different regions and classes might meet, do something useful together and discover more in common than they expected.
I think that possibility deserves consideration. It also deserves a more serious discussion than nostalgia for national service usually provides.
What would people actually do?
A useful programme needn't be military. There could be civic work, care or practical projects, provided the work was worthwhile and properly supported. The point would be to bring people together who would otherwise have little reason to meet.
We shouldn't assume that living in the same country achieves that by itself. Education, work and friendship can keep people within fairly narrow social circles. Institutions that require cooperation across those circles can provide experiences that an instruction to "be more cohesive" never will.
Nor should we romanticise the past. Earlier institutions didn't mix everyone equally, and sharing a workplace or a uniform didn't abolish class divisions. The question is what a new institution could genuinely achieve.
The objection to compulsion
Requiring a young person to give up months of their life is a serious restriction on their freedom. It can delay education or employment, disrupt care responsibilities and impose costs that fall unevenly. A badly run scheme might create resentment rather than trust.
Enthusiasm for a shared experience doesn't answer those objections. A proposal would have to explain why it required compulsion, what evidence supported its benefits and why a voluntary alternative wouldn't be enough.
It would also have to be genuinely shared. A scheme avoided by the well-connected and imposed on everyone else would teach precisely the wrong lesson about national obligation.
The wider point survives whether or not a service programme proves defensible. Trust across social divides needs opportunities for people to know and rely on one another. If we think those opportunities have weakened, we should ask what would replace them. We can't simply assume familiarity will develop while people lead increasingly separate lives.