The thesis is that we are already living in mouse Utopia, and that this will become more and more apparent until its reality will become... well, I was going to say 'undeniable' but that is silly: people can and do deny the most obvious things, and the process of population wide and cumulative mutational damage of the genome is certainly not obvious; but rather, at present, invisible.
So Mouse Utopia will never be undeniable, and indeed it is likely that the vast majority of mankind will never know what has hit them, and continues to hit them; nor will it ever be easy to disentangle the effects of genetic damage from other causes of maladaptive behaviour and disease. But at any rate, let's just say that the hypothesis of mutational accumulation in the human species will presumably gather more and more consistent evidence as time goes by.
What will life be like in Mouse Utopia? In The Narrow Roads of Gene Land Volume 2, WD Hamilton partially described that world in a chapter entitled The Hospitals are coming, and that is perhaps a good starting point - the idea that everyone will be damaged and most will be sick, in one way or another; so that life will resemble a hospital in which (some of) the less-sick (or the damaged but not-yet sick) tend the more-sick, as best they may - in intervals between doing whatever it takes to stay alive.
But this is not by any means an unusual or unprecedented situation for humans through much of the history of the species. For much of the time, Malthusian mechanisms have been in force, and populations have been limited by various combinations of starvation and infectious disease. Infections - in particular - have sometimes been endemic at a high prevalence, so that the majority or even all of the population might be suffering from, be affected by, some chronic parasitic disease - but at a relatively low degree of severity.
And with respect to the Mouse Utopia society being a Hospital, it is important to recognize that much of the pathology will be psychiatric rather than physical - this can be seen from the fact that the problems of the original Mouse Utopia were most behavioural rather than physical; and it follows from the fact that the highly complex human brain is exceptionally sensitive to random mutational damage.
Intelligence is probably damaged by mutation accumulation in an incremental and quantitative fashion - the more mutations, the more the lowering of intelligence. Therefore, decline of intelligence as mutations accumulate is likely to be relative smooth (rather than step-like).
But intelligence is 'general' intelligence, and is unusual in being a general attribute of cognitive function - it roughly corresponds to speed of processing, or coordinated functional efficiency. By contrast, most psychological functions are specific; and genetic damage is likely to be more qualitative and either step-like, or all-or-nothing.
What I think would happen, is that accumulating mutation damage would most likely show-up as varieties of specific brain functional damage leading to specific behavioural impairments of a social and sexual type - in a general context of continuing declining intelligence. (See reference below)
The kind of damage I am talking about represents a decline in functional adaptation of the human organism to its environment (its sexual, social and surrounding environment) - that is, a loss of effective functionality. This represents a decline in fitness, but not just relative fitness (because it is happening throughout the population) - it is a decline in group fitness - ultimately in species fitness.
If fitness is measured in terms of the capacity to raise sufficient viable offspring in a given environment; then the sexual and social changes induced by mutation accumulation will be such as to reduce the probability of doing this: partly by damage causing reduced brain processing speed and efficiency (detectable as reduced intelligence) and partly by damage causing specific functional impairments (detectable as sexual and social pathologies).
So, Mouse Utopia will be not so much be a hospital of sick people with the less sick tending the more sick; but more like the less crazy looking after the more crazy: a case of the lunatics have taken over the asylum because there is nobody left but the lunatics - so everyone in Mouse Utopia is mad, more-or-less; but with the sanest and most sensible people in charge.
At least, that would be optimal.
If the world is a psychiatric hospital where everyone is socio-sexually dysfunctional to some extent, then the people running the hospital ought to be the most coherent of the patients. Indeed, sanity is probably more of a priority than high intelligence - since a moderately intelligent coherent person (at least arguably) makes a better leader than a more highly intelligent crazy.
However, for the past fifty years and increasingly, we have been getting a taste of something different; and most nations and large organizations are now being run by - not the least impaired people - but energetic incoherent semi-lunatics; because in a mass media democracy, that is what the more-seriously-crazed majority seem to want.
Democracy as a system for choosing government has never made much sense; mass democracy in a mass media addicted world makes even less sense; democracy in a lunatic asylum is... crazy.