Defense attorneys and their investigators also investigate crimes. This realization shows why the broadening the warrant requirement can have perverse outcomes.
Say you are defending a man accused of rape due to lack of consent. Let's also say that this is a false accusation that can be proven false because the accuser uploaded a video of the events which show consent to her Facebook account. Let's further say that the defense really wants access to this video. If a warrant is required, the defense can NEVER get it because there is no way under the law the defense can get a warrant (unlike a subpoena or court order).
Think about that for a minute. Everything that requires a warrant cannot be accessed by the defense, regardless of what is at stake (which is always life and liberty). Period.
PS: I'm not suggesting rape accusations are usually false. Just an example to illustrate the downside of a broad warrant requirement from someone who defends accused people.