Is a machine-based workout really so bad?

Hi alL!

I'm 5'1 and about 117 pounds. I've been cutting my body fat for a while and am now just starting out (pretty much from zero) with strength training to build some lean muscle mass.

I've really enjoyed the various upper and lower body machines at the gym that allow me to easily increase weight and keep my form. But most of what I read online is really negative about machine work in general. What's up with this? For someone who's not looking to significantly bulk, but rather to build a little mass, increase overall strength and establish a healthy lifestyle, are machines really all that bad?