It's an ethics thing, and always something that gets heated in the DIY community.
For the Decimator it's a very reasonably priced pedal and is currently commercially available. IMO building them and selling them would be ethically wrong.
Every pedal I have, I have built. I like building pedals. It's how you work out how they work and what they are. I would not have bought an Decimator, I don't really have a use for one. But I wanted to make one... I'll make one for me and Cleggy (who makes the pedals with me) and that's as far as it'd go.
Things that I consider are 'ok' is building and selling circuits that are no longer in production. However you're on shady ground is what you're on when you start replicating booootique pedals. A HUGE amount of them are variations on old circuits. Those, IMO, are fair game. They're just doing what any other DIYer is doing and complaining about it is stupid. Original pedals that are in production are verboten IMO for selling on. Make 'em for yourself by all means. But don't flog 'em.
However... we also have the vastly over priced or unobtainables. The money Klon's change hands for is frankly idiotic. No pedal is that good. However it is a very good pedal that few people can actually lay their hands on (you could buy my Merc off me for the prices I've seen them go for). I've made a few Klone's for people. If I was rampantly profiting out of them I'd almost feel guilty. But I'm not and in fact I've stopped anyhow. This I suspect is the bit that gets most people riled.
Selling odd one's to friends is ok IMO. Certainly if you're not taking the piss price wise. I literally charge for parts and time. I'm not making a living out of it, some people are and I woudn't like to see them losing out.
Certainly if I do eventually try to make a living out of it, I wouldn't have a problem with the DIY community making clones of any of our designs. In fact one that I fancy having a go flogging is out there already for others to build. The best boutique makers recognise this and support DIYers and DIYers in return tend to respect that. Those that kick off (usually the ones that have had their pedal de-gooped only to find it's another tube screamer...) really should wind their necks in a bit and realise that a bunch of pedal geeks isn't going to hurt their profits. Athough they might find the discovery of what their pedal actually is, a little embarrasing. Danelectro cloning your pedal and turning it out for £40 a pop will hurt your profits however... (this has happened more than once).
So for the Decimator, I'd say, yup, go for it. Make your own. But trundling out a batch and selling them on for profit, especially when you can snag one 2nd hand for £60 and not much more new, would be a little off-side.
A very important point was made on the Fuzz documentary. Gear's value to a musician is basically how much he can sell it on for when he needs the cash ;) Names sell, clones don't.
