Revisionary. LW has made much stronger statements about MWI than "should be taken seriously" .. it has used the language of "slam dunks".

One obvious way is to start with some things that are slam-dunks, and use them as anchors. Very few things qualify as slam-dunks. Cryonics doesn't rise to that level, since it involves social guesses and values, not just physicalism. I can think of only three slam-dunks off the top of my head:

Atheism: Yes. Many-worlds: Yes. "P-zombies": No. These aren't necessarily simple or easy for contrarians to work through, but the correctness seems as reliable as it gets.

Of course there are also slam-dunks like:

Natural selection: Yes. World Trade Center rigged with explosives: No.

Note also:

But there are also simpler things we could do using the same principle. Let's say we want to know whether the economy will recover, double-dip or crash. So we call up a thousand economists, ask each one "Do you have a strong opinion on whether the many-worlds interpretation is correct?", and see if the economists who have a strong opinion and answer "Yes" have a different average opinion from the average economist and from economists who say "No".