It would seem that using a shampoo or conditioner that has silicone in it is not detrimental for our health or that of our environment! But that is not a reason to not make some changes for the better.   
Silicone is the plastic-y polymer used in everything from conditioners to household caulking. is not a natural ingredient & has effects that are not conducive to natural healthy hair.                
Reading the label of your favourite or new product you may see any of these and many more variations:
Cyclomethicone, dimethicone copolyol, amodimethicones or dimethicone.                
There are silicones & silcones!                 
Some of the them such as cyclomethicone,  which will evaporate and not leave build up on your hair & dimethicone copolyol, which is actually a water-soluble silicone and provides very little build up, but is very expensive (and will increase the cost of the product)  are not as bad.            
The most commonly used silicone is dimethicone which is the cheapest & one you will see mostly on labels (in all its derivatives).               
 Silicone has downsides that are mostly to do with build-up on our hair and over time weighing our hair down. By nature, many silicones are hydrophobic, meaning they do not wash out easily, leaving hair feeling heavy & greasy at the end of the day.                
Once our hair gets greasy we will wash and style our hair more, so we are not helping to improve the condition of our hair over time.                
Our hair also gets unavoidable daily abuse from the weather, what we wear according to our hair style and the products we put on it, not to mention the hot tools some of us employ to get the results we want!

The silicone in products we are already using will make our hair sleek and shiny after heating it up with a hot iron or adding heat via a blow dryer. It gives a fantastic silky shiny finish BUT weighs the hair down though over time. Silicone makes it harder for colour to penetrate and also means that colour washes out quicker, conditioners or conditioning products are less  inclined to be able to penetrate as well into the hair shaft due to the coating of the silicone on our hair from prolonged use of dimethicone.        
Dimethicone is the hardest silicone to remove too. To see how your hair reacts to a silicone free based shampoo you will need to wash your hair for a few weeks to remove all the build-up of the dimethicone. Make sure you use a silicone free hair conditioner too, such as enviroCare Hair Conditioner and once you feel the added volume & how light your hair is that not using products with silicone in it gives, you will be pleasantly surprised.              
Like everything that we do, changing our personal care products means we have to allow for a settling in period and time for us to get used to the changes that the new products evoke. 
Often silicone free shampoos also have no sulphates, so the foaming ability is lower as well as the different 'comb slide' effects that  you may not get that dimethicone usually gives in a regular or usual brand.              
These conditions mean we 'feel' the difference while using the products, so time and a mental shift is needed sometimes.    
These changes are different to what we are used to, so patience and basking in the knowledge we are not pouring dimethicone or sulphates onto our head can only be better for it.