1: Ignoring the thermodynamical impossibilities (and the stupidity of comparing pure water at STP to blood at blood pressure), the human body doesn't work that way. The blood, once you start heating it (the flesh you're burning/melting through is an insulator) would coagulate - every heard of cautery (though it would be happening in a wide area)? And as your 'blade' moves through, the coagulated blood will begin to burn just like the rest of the flesh. The only way to boil blood is to do it evenly and slowly, by raising core temperature.
2a: That you are (somewhat) correct about, U_P - if the interior of the tube is hot enough (and the tube itself has sufficient thermal conductive properties), then it can reheat itself faster than heat is taken - depending on what it's in contact with. If you were to press it against something that can cool itself faster than your 'blade' can reheat itself, it will cool.
2b: this is what GWG is right about - the dispersion of the laser only lowers the amount of energy impacting on that specific spot. The battlesuit is still absorbing the full energy of the beam, just not as concentrated - oh, and your heated 'blade' will still have a larger contact area than the somewhat-dispersed laser beam - and will have a much, much lower rate of transfer of energy (as it relies on thermal conduction rather than thermal radiation).
3: Is this really something we should be arguing about? Really? Other than the fact that if he sets the temperature up too much, it'll simply kill anyone in an area by being near them with it active?
4: Hard knowledge is critical to proper inventiveness - why do you think we teach engineers as much, if not more (since it's more varied and still as in-depth) science than scientists? I should know - I'm an engineering student, working towards a base of mechanical before specializing into nuclear.
5: PW does require a large degree of realism. And, realistically, as it stands - your design sucks. It could be improved a lot - but you don't really seem to care, preferring aesthetics. Also, if you ever want to have it, you not only have to pass the Armoury Master - you're probably going to have to pass me. Oh, and just so you know - hitting a target too hard with this would just bounce it or break it (or, if it's strong enough, the target's bones). Heat takes time.
6: This is all I'm going to say on the matter, unless U_P comes up with questions about it rather than just saying he's right and I'm not. GWG, I would advise you leave it too - you've already been muted a few times, let's not endanger more.