Prop G will be a retroactive tax applied to anyone who bought a multi unit building in SF in the last few years who would sell it the next few years. Tenants have no problem pushing this bill stating that buying a building does not entitle you to a lifelong contract and that 'things can change' which will negatively effect you. So even though you bought a building a year ago with no hint it could be taxed at 25%, you are now expected to pay that tax if you sell.
Now, on the other hand we have tenants who are upset that they have to leave their homes they (wrongly) assumed they could rent in forever. Either this is from ellis, OMI or other eviction. I feel for these people to a extent- But I am not a believer in the whole "right to stay in your birth city forever" movement. I do not believe anyone has any more of a right to live in San Francisco than they do Malibu or Aspen. It is one of the most expensive metros in the US.
If you are a 90 year old grandmother who was counting on your landlord not evicting the whole building, you should have known that was a risky bet to begin with. If you want to stay in a place forever you should buy the home. Otherwise, you need to be prepared to move should situations change. You need to prepare for all 'disasters' - That could be eviction, fire, death, floods, etc.. If you dont prepare, I will be sorry for you- But I dont think that entitles legal protection either. If you lose your house from a fire with no insurance, you are going to bare that burden alone.