There should be no intermediary between us and God. Please see Qur 39:3:
39:3 Absolutely, to God is the true system. Those who set up allies besides Him: “We only serve them so that they may bring us closer to God.” God will judge between them in what they dispute. Surely, God does not guide the one who is a liar, an ingrate.
These subtle forms of shirk are dangerous because people tend to not realize what they are doing. That is why many people on the DoJ will be surprised to know that what they have been doing was shirk. Their reaction would be:
6:23 Then, their only excuse was to say: “By God, our Lord, we were not polytheists!”
6:24 See how they lied to themselves; and that which they invented abandoned them.