Scientific theories, however, will ultimately be abandoned when evidence mounts against them.
Science is a human activity, and therefore subjective judgements are sometimes made.
It remains scientific, however, because subjective methodology and opinions can be questioned and criticized. This is how science progresses. Malthus observed the propensity of populations to grow exponentially if unchecked. However, real populations do not grow unchecked indefinitely because of competition for resources, predation, etc. Darwin read Malthus and realised that under such competition individuals which were better adapted to their environment would tend to leave more progeny.