I also hate the fact that people act as if only the elderly are vulnerable. Plenty if vulnerable people are in their thirties, so should they just die? What about their lives?
People behave like this because, as a general maxim, it's true. What's your evidence for saying that 'plenty' of vulnerable people are in their 30s?
There might be a lot of people in their 30s who were originally told they were vulnerable, and who had to shield. But, as we've learned more about the disease, we've realized that this was incorrect and the majority of these people have been redefined as not especially vulnerable.
In total 221 people in their 30s have died. I wouldn't say that this itself was 'plenty' from a population of 9 million in that age group. But, of course, some of these people will have been tragically unlucky, exposed to unusually high viral loads, or given bad treatment (eg unnecessary ventilation) at the beginning of the pandemic. The majority of them would not have been defined as vulnerable before they turned out to be.
Antibody studies show that about 5% of the UK population has been infected. In reality, then number will be higher because some people make immeasurably low levels of antibodies or had covid a while ago and the antibodies have declined. Probably 5-10% of the population has been exposed. (In London, it must be much higher given that antibodies were running at 16-17% at one point.)
The deaths that we've had don't represent a fair sampling of the 30s population. Some of those people will indeed have been very sick already, caught the virus in hospital etc. But say for the point of argument that the disease is just as lethal to the remaining 90% of the population as the 10% already exposed. That means that we could be looking at about 3000 deaths among people in their 30s, if every single person in the UK was exposed (itself very unlikely to happen). Most of those people wouldn't be understood before becoming ill as vulnerable.
If you're in your 30s, you're extremely unlikely to die of covid even if you have one or several comorbidities. Period.
You are, however, at high risk of losing your job, failing to pay your mortgage, being unable to manage the demands of childcare and work, or getting another illness which kills you after being poorly treated by the NHS. You're also at fairly high risk for mental health problems, addiction, and lifelong health conditions (like type 2 diabetes) that will mess up your long term happiness. So if you want to worry about 30-somethings, worry about all of that!