Nitric acid probably has the same effect. Still, nitric acid doesn't send messages. UA damaging ships doesn't mean UA are deliberately destructive, it could simply be a side effect of what they are (and as of now, nobody knows what they are really).
I figured the most likely purpose of the UAs in line with what we know so far was that they're basically sentry devices. Not defensive ones designed to destroy things, more a kind of guard dog. They're deployed in a shell around barnacle sites, they scan anything that approaches and we know they transmit a signal which depicts what they have scanned. The fact that
we can pick up and decipher that signal would be incidental; just because
we can receive it doesn't mean that it's actually being sent for
our benefit.
UAs damage anything which attempts to collect them as either a defensive mechanism to stop them being removed, or as merely an unintended consequence of their structure and/or method of operation, but I'd be much more inclined to believe the former, that it's an intentional design feature. The fact that they don't (for example) explode in a 50 megaton blast and instead just cause slow failure would support that hypothesis, in particular because they attack your cargo hatch - if they are intended to be deployed around a site to observe and report on anything approaching which could be deemed a threat, it would make sense that if captured they are designed primarily just to get free and resume operations, not destroy themselves in order to neutralise something which may not actually be a significant threat to begin with.
When a commander manages to circumvent those defences, removes a UA and transports it to a station, the UA continues to try to free itself; however since stations are significantly larger than a ship a single UA isn't able to do much of anything to it. Removing lots of them to the same station causes the station to begin to suffer partial failures once a critical mass of UAs has been accumulated there.
The barnacles seem to be automated biological factories which are used to produce materials. Perhaps they're a naturally occurring species that are just being used because they can produce valuable commodities (think cows or chickens) or perhaps they've been engineered, it's interesting to speculate but doesn't affect the hypothesis one way or the other really. I think they are deliberately seeded in an area with the right conditions for them to begin to produce meta-alloys and are left to operate with the UAs on guard duty. They are basically being farmed. The 'logo' that we've seen on them could be naturally occurring, or it could be the equivalent of a 'brand' (as in a burned-on mark identifying the 'owner' not a trademark) applied by whatever seeded that particular batch. Could show the location of origin of the batch of barnacles (think Jersey potatoes, or New Zealand lamb) the 'strain' of barnacles and what they are intended to produce (maybe there are others that we haven't seen yet which produce something other than meta-alloys) or the origin of whatever seeded them.
Of course, all that would imply that
something is monitoring the UAs transmissions. That same something would no doubt have realised that we found their barnacles and are currently shooting them up all over the Pleaides, stealing their resources and generally being unpleasant.
Extending the logic of them being farmed, if that was
my farm and I received a message that some pesky varmints were capturing my guard dogs and stealing my sheep, I know what I'd be doing. I'd be getting my shotgun and jumping in my pickup to deliver some righteous justice.
TL;DR - Thargoids incoming.