Why can you have one antivirus and many spyware programs?

I understand why you cannot have multiple anti virus programs but why can you have multiple spyware programs. I am confused because someone said that running multiple antivirus programs will cause both programs to fight over what to protect and what not to leaving the system not protected. Why isn't this the same with spyware programs...

I am looking for an answer from someone who is knowledgeable in this field. I don't want answers that say "oh I think this is why" I want a good answer...software experts...I am looking at you! If you don't "ANSWER" the question...that really is considered spamming (I think that is against the community guidelines!)

Why can you have one antivirus and many spyware programs?computers

The very specific reason for this difference between anti-virus and firewall verses anti-spyware is that the first two focuses on the entire system as a whole, having to embed deeply into the system files, bios, etc, while the anti-spyware major focus is on the browser point of entry.

Because the browser and email applications are one of the topmost layers of what comprises the computer, there can be several of these types of applications without causing interference or conflicts. The anti-spyware applications do not require such deep embedding into the system files, and so does not cause the same issues.

Now, anti-spyware programs these days usually have multiple actions to carry out, but the programmers make sure they do not overlap with the functions of the anti-virus and firewall applications functions. This is in order to ensure that there is little opportunity for a less experienced user to misunderstand the functions one carries out and accidentally crash the system.