That's what you think. It you are not doing anything illegal they wont act on it. Cross the line and they'll show you what they are capable of.IP address is an easy work around with a proxy.
Second, what would stop a criminal from using some other persons ID? or worse how would you regulate this in a foreign country?
Mobile is worse because you have a IMEI.A lot of people use mobile, and a lot of mobile users have shared IP addresses now. Short of MAC addresses, they are easily arguable in court.