Because you start out from the standard tech person position of arrogance. You didn't try to argue why you think his decision was ethically wrong. You went for a smug soundbite that sounds glib and clever.

1. He chose to join in 2007 - during the Afghanistan and Iraq wars. Those are both wars that, in my opinion and the opinion of many others (evident by the massive protests at the time) the British should not have been involved in.

2. In my opinion, anybody that joins the army when they aren't defending against an invasion (i.e. someone who travels thousands of miles to fight another country nowhere near their own) has a screw loose. There are times when fighting is necessary (e.g. WW2, Ukraine/Russia). There have been few of those times recently.

3. I have friends who have friends + relatives in the military. I've met those people at social events. I can't obviously say they represent all people in the military but the ones I've met have all been racist, homophobic and worse. Again, I believe you have to have a certain mentality to join the military when your country isn't actually at risk and this has been bore out by the people I've met.

4. The British military has committed countless crimes and atrocities over the last 50 years. I can't respect anyone who would decide to be part of that institution when it is not necessary to be.