...who else is using this indiscriminate method of killing?

So far as "suicide bombing" is concerned, the first people to carry it out in a consistent way were the Tamil Tigers in Sri Lanka (not a Muslim group - I mention that because at least one person posting on the Mudcat was under the misapprehension that they are).

Of course "indiscriminate methods of killing" have been widely used by people in conflicts all over the world, including governments, such as those of the UK and the USA and Israel (and many others), as well as by illegal organisations such as the IRA and ETA. Generally there has been widespread approval for this kind of things by otherwise humane supporters in the countries and communities from whom the killers come.

I can't see that indiscriminate killings, where the people who do the killing make every effort to reduce the danger that they will themselves be killed, are in some way more morally acceptable than those where the perpetrator knowingly dies in the act.