From a point of marketer, it's not that easy that you think. You need to know how to create strong accounts, warm them up and don't even think about it to use direct links for offers since your accounts will be banned instantly and if they are link your accounts together, your whole network will be banned. It can be done, but it's not that easy.
1. From a moral point of view, well if you download IG app you see that there are a couple of front permissions that you have control to turn ON/OFF: Camera, Storage, Location, WIFI, Microphone and some minor other ones, and that's about it what you can control what they have access about your phone. Or, not? Like on this list:
https://help.instagram.com/155833707900388 there is stated clearly that they can read: Device attributes, device operations, identifiers etc things that YOU are supposed to know about but you don't have the control over it. So, they can read everything about what you have on your phone, and you can't stop that, right? Is that moral?
2. SPAM = unsolicited message, right? This is the definition of the 'SPAM' term according to CAN Act. So, if you send a mail, sms, message to someone that didn't agree previously to receive that message is considered spam, nothing unclear till now. BUT.... If I get our right now and walk 5 mins with my eyes open and just look around, every 5 seconds I am exposed to an ad: billboards, flyers, windows adds, auditive sh*t and so on. Well, is that spam or not? Have I consent before getting out of my house to see those ads?!? NO!
Illegality: this is something you need to deal with. If your country decide that's illegal, then you can't do anything about it, it's illegal and that's it! But, trust me when I say that most of the countries don't give a flying f*ck if you send offers through social media, that's my 2 cents.