I don't think so, because this line of thought can leave room for people to fantasising about being "special" or unique in a wrong way. I mean like you owe something to the "cause", or you should sacrifice yourself for the good of others etc.

Probably someone with better theorical arguments can rescue me here. Lots of post left theory and egoistic theory use this revolutionary martyrdom as a counter example to criticize the "standart" social leftism

Maybe in some contexts is ok to elevate some people as "hero" ( better than martyr?), In order to help organize some resistance struggle or embody some group

I live for the things that I want, not die for them.
If I happen to die while living for the things that I want, that's fine with me.

If someone I have affinity with dies living for the things that we want, I can mark that without exalting them. I try already to carry the weight of all who I have affinity with in all my actions, and the memory of their lives lived can be a reminder of that.
But I won't call them martyrs, it's not my taste, too many bootlickers use it for bootlicking.

Martyrdom ever a good idea?

No. Suffering or dying for abstracts is never a good idea. It's an unfortunate consequence of opposition to power and not getting away with it.

Idolization of dead people can be a call to action, but it's hardly the only one.

Should his killers be considered martyrs

If they were caught and punished, they would be. If not, they can't be called martyrs by any definition.

In my opinion, it's a nested problem.

1. Dying for a message
2. Will the message cross
3. the honorification of the person. 3->1 here so bear with me.

(3) Will the person be honored or glorified for being a martyr, will their words be treated as infallible or their life untouchable? If we are to talk about Christianity, no, no it is not, we literally have multiple popes in history who are more likely to bed women than say mass sincerly. We have actual saints detailing their raunchy lifestyles coming toward a moral epiphany &c. Let's stick with one example, S. Paul. He killed a lot of christians, converted, got martyred himself. How many of the things in his letters alone could be seen as straying from the original message? PLENTY. Don't ask me, ask Martin Luther who used his letters as source material to dunk on the peasantry.

(2) Propaganda of the deed or Terrorism? It's a frequent question on this site and so far it's mostly been court of public opinion when talking about the subject as it is touchy. Will many people become anarchists by anarchist martyrdom? however can narrow things down. Sacco and Vanzanetti, so far, not really. It is niche and experience tells us it takes 300 years or more for it to work its magic and totally flip the morals & blubluh....

(1) Is dying for a message justified, no. kinda a consensus on that. Dying for any message dogmatizes it and more importantly treats it more towards a fucked reality necessitating the state. So no, just no.

so far 2nos & 1 quantum binary. kinda undecided as for me

I can't think of a cause that doesn't have martyrs, and I can think of many recent protests that wouldn't be as prominent as they were without them. Like it or not, the victims of oppression will be the face of anti-oppression.

In some cases, I think the post-left critique falls short. Martyrs don't have to be unique; they just have to represent a population in a useful way. A martyr can be anyone, so the message can just as easily be that they were a totally normal person. I think that there may be "healthier" cases of martyrdom when martyrs attain less prominence (and are consequently more difficult for mainstream politics to corrupt). Martyrdom in a close-knit community may motivate people to work together to accelerate the struggle, which I find desirable.

Is there a point where anti-fetishization becomes fetishized in post-left/anarchist theory? Methinks yes. That's why I prefer critical-self theory, which allows for some amount of purposeful hypocrisy, to post-leftism.

Edit: It's not like all martyrs are choosing to die for a cause. I might die at a protest, but that's not the same as going to a protest to die.

Lifting up people as special or better because they died is silly. Focus on their ideas if their ideas were good and try not to die

I guess it depends very much on the situation as there are many things to consider. In any case judge the action itself, not the person, don't create heroes. Follow ideas, not people. For example I, as a pacifist, highly admire if someone chooses to die rather than kill.

If I am not living to die in martyrdom, what's the point of living?