It can be an act of aggression (if I am building temples with the aim of wiping you out by means of dominion, which of course requires the addition of a lot of preaching or blood sacrificing or sceptic-swinging). Otherwise, it doesn't even have to be remotely close to unfriendly (as, for example, some temples that Morkilus and I both know about). People want their own lands to have their own dominions (when those dominions are good) and there's nothing aggressive about building the temples needed to accomplish this. It can require others to build temples in response, unless they don't mind having a weak or negative dominion in some of their provinces (which in some cases, e.g. bad scales, is actually nice).
In short, temples by themselves are not aggressive, not disrespectful, not even inconsiderate, unless there are other factors involved (a serious dominion-push, spells cast by the dominion-holder that hurt others in that dominion, etc.) In the absence of these factors, temples are nothing but expected.
I would say this even if I hadn't spent the design points on a Dominion of 8 and picked a nation with cheap temples amongst their strongest assets.
