If you have a portfolio of £1 million built up over 30 years, which is quite possible, you will have a capital gain of £400k and could pay CGT of £100k.

Only if you realise it all at once, how likely is that? Why are you making up fictional scenarios? Most rich people with significant assets are absolutely fine to have CGT equalised. Do you think that rich people are all evil? None of this changes the fact that there is potentially £6b from CGT