I’m sure you’ll notice that many people say they dislike WordPress for various reasons, such as bad security, a theme not working or their website becoming very slow.
In reality, WordPress is a great system — just like many other systems, no matter how small or large the website. The problems you hear about, like poor security, pages grinding to a halt or a bad user interfaces on the front end, are almost exclusively due to poorly coded plugins and themes.
As a result, the theme and plugins you choose matter a lot. You know how some people have really slow computers and complain about them all day? Then you take a look and see that they’ve installed every single piece of shady software available? The situation is kind of like that.
Coming across a theme or a plugin with malicious intent is pretty rare. More often than not, the problems one creates are caused by sloppiness or insufficient knowledge of coding standards.
What this all boils down to is this: Look for a theme and plugins with good reviews, a sizeable user base and an active development team. This will negate or minimize any negative impact on your website.