are limits. for example, if we could turn the oceans into fresh water, there would be some population of humans that would take up all the land and drink all the water. therefore, water and land are limited.
fact: can you imagine some amount of humans that the planet could not support? yes? 100 billion maybe? then there is a limit on population growth simply by amount of space if nothing else. we may not know exactly how many that is, but it is a scientific fact that there is one, somewhere between 6 billion and 100 billion. so it cannot be said that there is no limit to human population 