Looking at the first example it seems that this might discourage someone from voting for the return (large) proposal if they want to retain the full voting weight for the other smaller proposals. This may have an unintended effect of lower threshold of return (or burn, if exists) proposals.
Having the ability to vote against specific proposals may mitigate this which would allow preventing a particular proposal from being funded without affecting other proposals that a voter might abstain or vote for, even in a high participation scenario. The return proposal is expiring in 4.5 years and would be costly to recreate under the current fee structure so the best time to implement it would be before that expires.
That is a feature and not a bug. However, with the Ninja mine and our DAO Fund being nowhere near equilibrium I wrote in the maximum weight penalty as a function of participation. So you could vote for the return and your chosen proposals with no further weight reduction for the foreseeable future(DAO Funds will last over 30 years at current price and payout). Also means, that as long as a whole bunch of Stake voted for the most desirable proposal, a vote for that would effectively be voting for return as well as the max weight reduction would go down.
After looking at the code, I think downvotes would be a lot harder ask than the weighting system... and if we had down votes I believe they'd have to be weighted as well... and the overall effect might not be as strong as we want.
A large proposal like VP would need to get more backing as well... But if this was the paradigm I'd guess VP would set up a longer proposal to attract the right support.
I agree that we should formalize a return proposal in code instead of having somebody pay thousands to set up another decade of it. Would also be cool if we could do stabilizer at the base level. I think the return could be as easy as modifying the end date of proposal 0 at hardfork... a stabilizer would be a lot harder as consensus code means everybody would know what it's actions are and it could likely be gamed.