"just because your dutites": I was refering to your part where you said the ones you supported did exactly that...
"start internal wars and upset the order of things without your kings consent": but the vasal claims what is rightfully his (otherwise he wouldnt have a claim!)! He is not upsetting the order; you are.
"keeping order and helping someone like them": but you are doing it agaisnt someone like them as well... they might all have claims they wish to press.... If they could never expect you to stay out of internal affairs, whether it is them rewoking titles or them securing their de jure duchis or even pressing inheritance claims on their neighbourh, yoy become an unpredictble lord.
"should a neutral lord" how do we know they are neutral?
"an upstart got a thrashing by his king": maybe the one you are protecting is the upstart, and the other one is their cousin?
"in the name of preserving the peace?" They might not be interested in peace, as they can expand through war.... it is more honourable AND easier than doing it through plots anyway.
"when levy's are decimated and tax disrupted, that annoys me", tyes it anoyed medieval kings also, but it didnt prevent many, many, many, many small international feuds and wars, and sieges from happening. TRry reading for example something of the history of any kingdom or duchy in the German holy roman empire - the emperor generally did not get involved unless it touched upon his own rights.
"And if it does come to blows the king should be able to intervene by force during the conflict if he so chooses." Yes the kings think that, but why should the vasals? That PREVENTS them from achieving their goals?
There are basically 4 types of vasal wars (I choose dukedom titles for the ease, the same goes for kingdom tier vasals):
1. Rebellions from counts against a duke: his job is to protect said region, if he isnt strong enough he isnt strong enough - dont get involved
2. Two dukes fighting over a county: they both have claims if you interfere you are breaking your oath to at least one vasal.
3. Two people have claims to a dukedom and fight over it: they both have claims who is to say who is the TRUE claimant? The other vasals will not think it should be you, because who will you support next time?
4. A duke fabricate a claim on a neighbourgh: this might seem like the place to join, but this cannot be done when the claim is made as know it is recognised he has the claim. IF you spot him plotting to fabricate it you can imprison him or make him stop.