We want our systems to be run with good protection, be it Windows, MAC OS, or Linux. However, it's Windows that's mostly affected by malware simply because it's the most commonly used OS and therefore most targeted.
Although there are malware, ransom malware already exist on MAC OS today and they should be protected with an antimalware solution.
Now, one thing all OS naturally have in common is that when running antimalware, they tend to get slowed down. That is the side effect of running a security product and real-time scanning for malware code on the computer. There is simply no way around this, besides making smarter and better algorithms using the smallest amount of compute power, network, and disk utilization. The same goes for the encryption of data traffic over network connections, simply to block anyone from listening in on the communication or tap any data, this will also slow down the speed. Because it's impossible...