The linked thread considers a case where the alternative $H_1$ and the corresponding rejection region are chosen after the test statistic has been observed. This is bad practice as it distorts the $p$-value and may change the decision (in comparison to the valid way of conducting the test). Now if you choose $H_1$ before observing the test statistic, the problematic aspect of the former approach is eliminated.
One-sided tests exist and can be used and yield valid results. If you know $\theta<c$ to be impossible, you can formulate and test $H_0\colon \ \theta=c$ against a one-sided alternative $H_1\colon \ \theta>c$ no problem. Regarding power, indeed it would be a waste of time to employ the two-sided $H_1\colon \ \neq c$ instead. However, if $\theta<c$ is merely unlikely according to our understanding / is out of line with our favourite theory, this is usually not deemed sufficient to exclude this possibility from the alternative.
Regarding references, I think this is introductory level material and should be found in most classical textbooks, both theoretical and applied. A list of free statistics textbooks is available in this thread. This one contains some more (not necessarily free).
