There have always been people who could get very sick and even die if they were to catch anyone of a number of viruses that circulate every year. No one suggested everyone should give up their right to personal liberty to prevent that.
It isn't just people who are vulnerable. The reality is, we aren't practised in treating Covid-19 and, as it is newly spreading in humans, everyone is at risk -- including you and your parents. Giving up your liberty is to protect yourself too, but I think it's a shame if you can't show empathy for those who need extra protection atm.
There have always been people who are killed on the roads every year. No one suggested that non essential car journeys should be banned to reduce or prevent this.
We have restrictions on who can drive, including restrictions around age, drivers proven to be dangerous who've had a license revoked, some MH problems, some physical health problems etc. We also have continously improved safety to protect people. You are asked to stick to a speed limit, not drive under the influence etc. Those ARE restrictions on complete liberty (where you could drive wherever on the road with no limit, no belts, no airbag, no child seat at any age, even if you were having seizures 8 times an hour).
Why are people with cancer's lives seen as less worth saving than those who might catch Covid?
There are difficulties around this topic. However, part of the planning around cancer treatments were to not expose patients already at risk to Covid-19 or damage their immune system (using chemo) at a time when they are very likely to need that immune system.
Why are people OK with this?
Because sometimes these things happen and difficult times crop up. I don't find it particularly awful to follow a few rules for the time period Covid-19 is putting everyone at risk. I've gone through an amount of serious trauma in my life -- and wearing a mask and staying at home don't come anywhere near those experiences. I'm happy to contribute to slowing spread by a year or two with stricter isolation regulations, though I miss friends. I don't support the way it's been handled by the Gov and have raised this where I felt appropriate. I also recognise I have no place to moan at all comparatively to many, in fact I'm very lucky to be in the position I am in. Although we have lost an older, much loved family member and couldn't see them or attend the funeral (distance and number restrictions, no remote connection was available), and that was very sad, in most ways otherwise we've been very lucky. I focus on trying to do the best I can, adding in activities I can and so on. We camped out in the garden over the summer (aware it's not possible for everyone), I set up treasure hunts and cinema nights at home (rain), went for nice big woodland walks etc. I find the best way to be resilient is to try and break negative thought patterns through distraction and focus on positive things you can do. If you acknowledge negative thoughts, but don't dwell on them, it can really help. Mindfulness can be useful. If you can't break out of negative thought patterns and worry the whole situation is affecting you seriously, try and access help. It is difficult at the moment, but there are routes outside of GPs (charities as well as private for those who can't pay) that can sometimes give really good advice/coping strategies.
How can the government make it illegal for me to see my parents?
Because it's for a short period of time in the grand scheme of things. It also depends where you/your parents are, how many are in your family etc. There are some options, though they don't and can't suit everyone. Technically, your parents could move in with you and you'd see them then. Yes, it's frustrating and sad, but we're all in the same boat. This isn't a usual situation. You could give your parents Covid-19 and one or both could die, that would (one would assume) be very difficult to deal with if you knew you were probably to blame. There are no easy answers as the whole thing is complex, but without some restrictions there's no protection. It's important to remember that catching Covid-19 would also take away your liberty, possibly in a far more damaging way.