I'd say it's because about 80% of people in your age group (12 - 14) are jerks and immature with these sort of things. It's the hormones way they saw some other cool idiotic famous kids do things and they decide to follow it and try and be cool. If you don't believe me, just play an online game. The things some of these kids say are just horrible.
I think love is a great thing. But people should figure out if they are confused and if they know the difference between love and lust before taking it any further. To that, I'd respond first by citing the subjectivity of the term "love," and then by saying that a good 90% of adults don't seem to understand the difference themselves (most marriages these days aren't happy, and many end in divorce).
Honestly, all that doesn't even matter anyway. If you think you like someone, go for it. The kind of people that would make belittle you for something like that aren't the people you really want as friends, I'd say.
As it turns out, there are more important things than your reputation at school, and I really mean this.
Moreover, after the people who are around you reach the age of 15 or so, these immature views start vanishing anyways, and they'll forget about all these bullying in entirety, so it's better if you ignore them.