Prevent/Reduce/Detect fake (already know) connections

If you get a suspicious group link sent to you, the only thing you can do is report the group link creator as a spammer. If you click the link and don’t report the creator, then yes, there could be a mix of attackers and victims in the group, and you will be sharing your profile.

Why can’t you click a group link and report it as spam (i.e. just the creator of the link) before you share your profile or see anyone in the group connection?

I agree, the other attackers in the group could avoid being punished for spamming, since they would only appear once the victim has already shared their profile. Is that your point?

Yes, the group creator can simply be not main attacker but an account with no connection. The bots created for phishing already know connections can join after you.