I'd guess there's like a 60% chance of success, but that's just from experience watching SpaceX development/launches. I'm really hoping it goes well also
The booster actually hasn't "landed and then blown up" before, but you are correct, there have been failures. The soft landings in the ocean was not meant for recovery, only to test if the booster and ship could slow themselves sufficiently after surviving reentry. The main point you seem to misunderstand is that the approach SpaceX uses is called "irritative testing" they are expecting/welcoming failures during testing so they can improve/fix the points of failure (like Edison and the lightbulb). Like you said, NASA would not be celebrating a launch explosion/failure because NASA does not use this "iterative testing" approach and instead relies on very precise expensive engineering so that everything goes right on the first try. The downside is this means it takes much longer for NASA to design and produce a rocket. Both approaches have pros and cons, but it's important to understand that they're very different. As for bringing supplies to Mars, that's a whole different discussion, but it all comes down to being able to launch enough mass to sustain a mission with redundancy which starship aims to do once it's fully operational.
On another note, I totally understand being critical of starship/SpaceX especially if starship has failures when it's launching actual payloads for official missions, but for now there's a reason they're called flight tests and not missions. There's no payload and no guarantee of success. But from SpaceX's track record with falcon 9, it's reasonable that they will get starship fully operational soon.
I still respect your opinions and willingness to share them even if I don't agree.