The possible harm done to your nails by gel polish has a lot to do with the way it's applied and the way it's removed. Many salons will rough up the top of your nail by filing it aggressively. They do this in hopes of creating a velcro-type surface which means that the gel will grab your nail more and you will get a lot longer wear. I can't tell you how many ladies I know that claim they get 4 weeks of wear out of their gel polish but yet complain about how their nails are thin and sensitive to the point they have to take breaks from gel frequently. Then during removal a lot of places just file the gel off with an electric file or they soak it for 3 seconds and then start scraping and buffing until it comes off. So yes you may get 4 weeks of wear with this method but you're also going to end up with super thin and unhealthy nails that need to be grown out before you can go back to gel. These methods of application and removal are not healthy, and if your current salon does it this way I would stop going there.
The other extreme are people that constantly complain about how gel polish is full of chemicals and the uv curing and acetone soaking off process is sooooo bad for you. First off all the horror stories that people talk about are usually either extremely exaggerated urban legends or they're based on crazy people that were doing their nails 5 times a day and ended up suffering the consequences (similar to people who fake bake every day and get skin cancer...duh!). If you're really that concerned about chemicals and uv exposure then I would suggest not doing your nails at all. Even water based nail polish has some chemicals in it and non-toxic only means that the levels of the chemicals are considered too low to be harmful. At the end of the day you're putting something foreign on your body. There's really no such thing as natural nail polish or gel. (click here to see my previous post about UV exposure during gel application for more details)
My personal opinion lies somewhere in the middle. I am a firm believer in moderation. Gel polish does not harm your nails if it is done responsibly. I take care in the products I use on myself and choose for the salon. I look for products of high quality, low toxicity, and also flexibility. This means that our clients' nails stay healthy and strong and they can wear gel as many times in a row as they would like without any adverse effects. The gel polish we apply may not last 4 weeks but I'd rather focus on the long term health of our clients' nails than try to make sure the stuff stays on forever. Soak-off gel polish is not supposed to last 4 weeks. It usually lasts 10-17 days depending on the person before it starts chipping and/or lifting with most people being around the 10 day mark. But this is normal and means that when you do decide to change your color, you'll still have healthy nails underneath and the gel will be able to easily be removed and reapplied.
Would you rather have 4 weeks of wear but only be able to wear gel once or twice in a row before you have to take a break and grow out your nails, or would you rather have 2 weeks of wear but be able to switch up the color and keep on wearing gel with no problems?! I prefer the latter.