Although, I could generally agree, the circumstances surrounding Acts 21 and how Paul was specifically ordered by the other Apostles to go up to the Temple to demonstrate how he was, in fact, not operating contrary to the law suggest to me that there was something more going on here than just, in this instance at least, going because that's where people were gathering.The apostles may simply have kept attending the Temple because that's where they would find people to talk to about God. When going to towns outside Jerusalem, the apostles also went to the synagogues first, same reason. Same reason many of us go along to churches we disagree with either regularly or as occasional visitors - because of the people, our visit does not necessarily imply agreement with all details of that churches doctrine and practice. It MAY imply that, but it does not necessarily imply that.
No problem discussing this here! It's a worthwhile topic to discuss as so many people are getting enthusiastic about it, while so many others have very serious concerns. Good to raise it.