It is a tax on all users

No it is not. If you have literally no STEEM or SP (which is possible, since zero SP accounts now get some RC allowance), neither the value of your stake nor your share of ownership of the total supply declines as a result of inflation.

For everyone else, the effect is proportional. Someone with 1000x more stake is paying 1000x more.

Especially also now content creators 'pay' with lower post rewards

No, stakeholders pay all content rewards via inflation too. Content creators receive content rewards. There is a huge difference. What happened with the enacting of SPS was that a share of inflation that stakeholders pay to content rewards was shifted to SPS. Either way it is still stakeholders paying it.

inflation impacts you anyway, if you vote for any proposal or not.

Sure, but I'm absolutely going to vote in a manner that I believe spends (or does not immediately spend) those inflationary rewards in the manner that gets stakeholders the best value for the cost. If i lose the vote, fair enough, I can sell my stake or accept the disagreement and recognize that you win some and lose some.