addictive?

Hell, no. It's pretty much the opposite, in fact. Psyloci(bi)n and LSD are pretty hard going, and the higher the dose you take, the more likely you are to have an unpleasant trip. It can be pleasant at low enough doses, but going overboard can make you feel like you're losing your mind, dying, or that the world is out to get you, trigger depressive or psychotic episodes, etc. (ie, "the bad trip"). For most people (particularly those that like to feel in control of themselves, or have borderline psychological problems that are just about in check), that's something that they'll never want to repeat. So in that sense, it's got the opposite profile of most other stimulant drugs which, once you've got a taste of them, you want more.

There's also the issue of recovery time. Having your brain switched into a higher gear like this, with no way of turning it off except to ride it out can be very mentally tiring. Not so many people would want to take these drugs again the following day. Fewer still have the inclination (or the time; you're talking about "losing" 6--8 hours for each trip and comedown time, longer if it's LSD) to go on an extended binge, and even that (IME) tends to be self-limiting, as you need more recovery time. A week or two (when mushies are in season, natch) of taking something every second day seems like a practical limit, and even then you'll find people end up taking smaller doses so they can pace themselves and not get too out of it.

Of course YMMV, and I wouldn't recommend anyone who's unsure of what they're doing or doesn't have supportive friends they can turn to in case anything should go wrong to seek these out. You might have a very bad experience you will regret. Or you might be the one person in 100,000 (completely made-up figure) with just the wrong sort of personality or brain chemistry that finds they can become addicted to shrooms. The latter is highly unlikely, IMO, but I'd never say never.

Personally, getting back to the article itself, I think the main problem with psychedelic drugs of any kind isn't the drug itself, but society and societal contexts for drug-taking (the two feed into one another---making the drugs illegal makes it more likely that the context for drug-taking involves more criminality and abuse, which feeds society's condemntion and ostracisation, which feeds ...). I'm not going to go all hippy and say everyone should take drugs (they shouldn't), but I do think society needs more "grown up" attitudes to drug-taking. That means, among other things, treating people like adults and letting them make up their own minds instead of treating them like children, stop using hyperbolic scare stories and start giving proper, non-judgemental advice on drug safety rather than treating the user as a criminal, and admit that we've been using drugs for millennia and that prohibition has never worked and never will... Many cultures have managed to incorporate use of psychedelics into their societies in the same way that some of our cultures have managed to develop fairly sensible attitudes to alcohol (while others, and other individuals) have not. I just think that there is definitely a need and a possibility for a more enlightened stance regarding the use of all drugs in society. Treat shrooms as a "special medicine" and not as an "illegal chemical" (the same goes for lawmakers and users here).