There is absolutely nothing immoral about this. In fact, it's perfectly consistent with our morals. Our morals only apply when one of our citizens are victims. On our soil, perpetrators of heinous acts will be held reponsible for their actions. But selling arms to Saudi? That brings big money into our economy, and bringing big money into our economy is morally favourable, even though it arouses bloodshed, and polticial and economic instability for the victim's country, because the victims aren't on our soil. Sure, you may attempt to counter this by saying that our condemnation of violence should be applied universally, as the principle of suffering is not constrained by geography. This argument, however, can be dismantled simply by acknowledging that the money is used to support our systems (and the costs), which are far superior to anything of close resemblance in these measly third-world countries. The money goes into our system, which reduces our suffering, and therefore it's justifiable. Why is the alleviation of our suffering (which may seem to be trivial to theirs in comparison) at the expense of their lives justifiable? It's simple really. It's because we're great, and they're not.

It's impossible to understand the strong sentiments harbored by these people against our great country. Do they not see how great our system is compared to theirs? Do they not see how well we've used the money which financed their destabilization? They're simply jealous of us.
Thank god for brexit, we can stop these unreasonable hypocrites from coming in.