With no armour anything can hurt you... fragments, bullets etc, but at the other end there is no level of armour that will protect you from anything and once you invent your armour your enemy is going to start to find ways to defeat it so even if you are protected you are likely only safe for a short period of time before they work on a solution.
The BTR series of vehicles were made fun of because of their light armour, but even their light armour was better than riding in the back of 2 ton trucks... it comes down to value for money.
They could have gone with tank level protection but that would be too expensive so most would end up walking which means you lose mobility which was a serious problem for the Germans in WWII. It might look like the Germans were a fully mechanised force but the tank forces were mechanised their infantry was not and nor was most of their artillery... which is why they had Stukas... the only artillery they had that could keep up with their tanks.
The point is that a BTR-60 protected them from small arms fire coming from a distance, it made them very mobile and it had a turret with machine guns the equivalent of a light cannon. On a scale it didn't protect from a whole lot but it was cheap enough for everyone they couldn't put in a BMP to have one so they were actually fully mechanised much faster than the west was. (in significant sized armies obviously.... a small force like the New Zealand Army could be all mechanised easily because there are only 5,000 soldiers...).
Things like ERA and APS were solutions to the problems of defeating rather heavy weapons without having to resort to super heavy armour, and they were clever solutions that could be applied fairly easily and were effective against the vast majority of weapons tanks will face... RPGs and ATGMs... but not so good for IEDs. But there are other things for those...
The point is that the advantage of the BTR was not its armour, but the other things it brought.... mobility and fire power and speed, with more protection than they would get from a truck, but at a price rather similar to that of a truck so you could afford to replace the troop transport role of the truck with something that was amphibious and armoured and armed. It was no MRAP but photos of them with missing wheels in Afghanistan show they can take a hit and keep moving...
In the case of these vehicles even if it just means the enemy see the vehicle and have to take some time to work out where a weak spot might be to launch an attack might mean they don't end up with time for a shot, or they pick a bad place to shoot at in panic.